The cultivation of plants in a nutrient solution rather than in the soil.

(chemistry) A chemical process of decomposition involving the splitting of a bond and the addition of the hydrogen cation and the hydroxide anion of water.

(inorganic chemistry) a colourless gas with molecular formula HI, having a suffocating smell; it forms hydriodic acid when dissolved in water

(inorganic chemistry) A colourless gas having an irritating smell; it has the molecular formula HBr, and dissolves in water to form hydrobromic acid; it has many industrial applications including the production of barbiturates and synthetic hormones.

(chemistry) a colourless fuming liquid or gas, having a molecular formula of HF; it dissolves in water to form hydrofluoric acid and has many industrial uses including the production of Teflon and the refining of uranium; it corrodes skin, flesh and bone, and any skin contact must be avoided

(inorganic chemistry) A colourless, very poisonous, volatile liquid, HCN, used in the production of dyes, plastics and fumigants; it dissolves in water to form hydrocyanic acid and reacts with bases to form cyanides, and with some organic compounds to form nitriles.

(chemistry) a solution of hydrogen cyanide, HCN, in water; a weak poisonous acid, used as a fumigant

(physics, chemistry) An electrode with a standard electrode potential of zero; used as a standard against which other electrodes are measured.

(Greek mythology) A mythological serpent with many heads, slain by Hercules as one of his twelve labours.

(inorganic chemistry) A colourless liquid, H₂O₂, soluble in water, used as a mild antiseptic, bleaching agent (especially for bleaching hair), oxidizing agent and chemical reagent.