Of mixed origin or composition.
Hybrid Bearing
A bearing that consists of metal rings and ceramic balls.
Hybrid Circuit
A circuit made with a mixture of passive and active components.
Hybrid Composite
A composite with two or more reinforcing fibres.
Hybrid Electric Vehicle
A vehicle powered by two or more energy sources, one of which is electricity.
Hybrid IC
Two or more integrated circuit types, or one or more integrated circuit types and discrete components on a single substrate.
Hybrid Orbitals
The combination of a set of atomic orbitals to produce a new set of hybrid orbitals.
Hybrid Vehicle
A vehicle that combines a conventional propulsion system and a rechargeable energy storage system.
The old name for Mercury and from where the chemical symbol Hg was derived.
A compound that has discrete water molecules combined with it.
Hydrated Beryllia
Alternative name for Beryllium Hydroxide.
The combination of water and another substance to produce a single product.
Hydration Number
The number of water molecules associated with an ion in the process of solvation in aqueous solutions.
Hydraulic Fluid
Fluid serving as the power transmission medium in a hydraulic system.
Hydraulic Motor
A device which converts hydraulic fluid power into mechanical force and motion by transfer of flow under pressure.
Hydraulic Pump
A device which converts mechanical force and motion into hydraulic fluid power by means of producing flow.
Hydraulic Set Cement
A cement that sets through reaction with water.
Hydraulic System
A system designed to transmit power through a liquid medium permitting multiplication of force.
Hydraulically-Assisted Clutch
A clutch operated by hydraulic pressure.
Engineering science pertaining to liquid pressure and flow.


A colourless, fuming, corrosive liquid that is a powerful reducing agent.

A compound containing a negatively charged hydrogen.
Hydro Turbine
A rotary engine whose energy is generated from moving water.
A chemical containing only hydrogen and carbon.
Hydrochloric Acid


A solution of hydrogen chloride in water. Concentrated acid is a colourless, fuming, corrosive liquid.

Alternative name for Hydrogen Chloride.
Hydrocyanic Acid
A solution of Hydrogen Cyanide in water.
Hydrodynamic Bearing
A bearing which supports the shaft on a thin film of oil, the fluid-film layer is generated by journal rotation.
Hydrodynamic Lubrication
A lubrication film completely separates two load-bearing surfaces.
Production of electricity by water power.
Hydrofluoric Acid


Aqueous solution of hydrogen fluoride. Dissolves most metals and etches glass.

A manufacturing process that involves pumping fluid into a die, so that the pressure will expand a tubular blank to take the form of the die.
The least dense element. It has metallic and non-metallic properties.
Hydrogen Arsenide


Intensely poisonous colourless gas. Also known as Arsine.

Hydrogen Bonding
Strong type of intermolecular dipole-dipole attraction. Occurs between hydrogen and fluorine, oxygen or nitrogen.
Hydrogen Brazing
A method of furnace brazing in a hydrogen atmosphere.
Hydrogen Burning
Hydrogen burning is the fusion of four hydrogen nuclei into a single helium nucleus.
Hydrogen Carboxylic Acid
Another name for Methanoic Acid.
Hydrogen Chloride
Dissolves in water to produce hydrochloric acid.
Hydrogen Cyanide


Colorless, very poisonous and highly volatile liquid.

Hydrogen Economy
A scenario where the world uses hydrogen as the primary energy carrier in place of fossil fuels.
Hydrogen Embrittlement
A process which results in a decrease of the toughness or ductility of a metal due to absorption of hydrogen.
Hydrogen Fuelled Vehicle
A vehicle that uses hydrogen stored onboard as the energy source for motive power.
Hydrogen I Nitride
Modern name for Ammonia.
Hydrogen I Selenide


Colourless gas.

Hydrogen I Telluride


Colourless gas.

Hydrogen Iodide


Colourless gas.

Hydrogen Peroxide


A colourless, viscous, unstable liquid compound of hydrogen and water with oxidising and reducing properties. Used for bleaching wool, silk, linens, furs and hair products since the 19th century. During the Second World War hydrogen peroxide was used as a propellant in V1 rockets and was subsequently also used as a propellant for submarines. Hydrogen peroxide is also used as a preservative and disinfectant and is used by archaeologists to dissolve clay from finds.

Hydrogen Persulphide


Colourless liquid.

Hydrogen Rich Fuel
A fuel that contains a significant amount of hydrogen.
Hydrogen Storage
There are types of hydrogen storage: compressed gas, liquid or chemical.
Hydrogen Sulphide
Poisonous and smells of rotten eggs.
A chemical reaction in which hydrogen is added to a compound.
Hydroiodic Acid
Alternative name for Hydrogen Iodide.
Hydrologic Cycle
The cycle of water from evaporation through condensation to precipitation.
When water reacts with another substance and as a result the oxygen in water makes a bond with the substance.
An instrument used for measuring the specific gravity of a liquid.
Hydronic Heating System
A system that circulates heated water through convectors to heat a building or given space.
Hydronic System
A re-circulating water system used for heating and/or comfort cooling.
A polar molecule or group that can form strong hydrogen bonds with water.
A nonpolar molecule or group that has little affinity for water.
A hydrophone converts acoustic energy into electrical energy and is used in underwater passive systems for listening only.
A reducing agent used in photographic developers.

All the water on the surface of a planet.
Hydrostatic Bearing
A bearing which supports the shaft on a thin film of oil, the fluid-film layer is generated by externally applied pressure.
Hydrostatic Lubrication
A system of lubrication in which the lubricant is supplied under sufficient external pressure to separate the opposing surfaces by a fluid film.
Hydrostatic Pressure
The pressure at any point in a liquid at rest; equal to the depth of the liquid multiplied by its density.
Pertains to hot water or the action of heated water, often considered heated by magma or in association with magma.
Hydrothermal Alteration
Alteration of rocks or minerals by the reaction of hot water with pre-existing rocks.
Movement of a plant in response to water.
A substance that contains water. The opposite of anhydrous.
The OH- ion or compounds containing the OH- ion.
Hydroxy Group
An -OH group attached to an organic molecule.
Hydroxybutanedioic Acid


An organic dicarboxylic acid extracted from apples and various other fruits.

An electrical instrument designed to measure the water vapour in the atmosphere by using a material whose electrical resistance varies with atmospheric humidity.
A recording-type hygrometer.that produces a permanent hygrogram.
A tool for measuring the humidity of the air.
Able to absorb moisture from air.
Disturbances in the body resulting from an excess of the ambient pressure over that within the body fluids, tissues, and cavities.
An open curve with two branches, all points of which have a constant difference in distance from two fixed points called focuses.
Hyperbolic Sine
Hyperbolic sine of x.
Hyperbolic Spiral
The curve whose equation in polar coordinates is r*theta=a.
A geometric solid whose equation is x2/a2+y2/b2-z2/c2=1 or x2/a2+y2/b2-z2/c2=-1.
Hypereutectic Alloy
Any binary alloy whose composition lies to the right of the eutectic on an equilibrium diagram, and which contains some eutectic structure.
Hypergolic Mixture
An oxidizing agent and a fuel that react or ignite instantly and spontaneously on contact.
Any kind of link on a webpage.
Farsightedness. Images of distant objects are formed beyond the retina.
A condition in which the total oxygen content of the body is increased above that normally existing at sea level.
A range of speed that is five times or more the speed of sound in air.
HyperText Markup Language
The system used for creating World Wide Web pages, ordinary text with commands for special effects like pictures, colour and links enclosed between < > symbols.
HyperText Transfer Protocol
The protocol computers use to send web pages over the internet.
A solution which has higher osmotic pressure than some other solution.
A range of speed that is about 12 times or more the speed of sound in air.
Pertaining to low atmospheric pressure.
Disturbances resulting from a decrease of ambient pressure to less than that within the body fluids, tissues, and cavities.
Hypoeutectic Alloy
Any binary alloy whose composition lies to the left of the eutectic on an equilibrium diagram, and which contains some eutectic structure.
Hypoid Gear Lubricant
A gear lubricant having extreme pressure characteristics for use with a hypoid type of gear as in the differential of an automobile.
Hypoid Gears
Gears in which the pinion axis intersects the plane of the ring gear at a point below the ring-gear axle and above the outer edge of the ring gear, or above the ring-gear axle and below the outer edge of the ring gear.
The longest side of a right triangle.
A hypothesis is a proposed answer to a problem, or an explanation that accounts for a set of facts and that can be tested by further experimentation and observation.
Hypothesis Tests
Tests based on a sample of data to determine which of two different states of nature is true.
If the input varies from an initial point to a final point and then retraces its value back to the initial point, then the two paths of the output should be identical. If there is hysteresis in the system then the output paths will not coincide.
Hysteresis Damping
Hysteresis damping produces a force which is in phase with the velocity and proportional to the displacement, resulting in a linear equation of motion.
Hysteresis Loss
The power loss in an iron-core transformer or other alternating-current device as a result of magnetic hysteresis.