(biology) A marine hydroid of the genus Hydractinia or a closely-related genus

(hydraulics, surface science) For a porous material, the ratio of porosity (ratio of volume of interstitial space filled with fluid to volume of material) to specific surface area (ratio of surface area in contact with fluid to volume of material); for a pipe or channel, the ratio of cross-sectional area to wetted perimeter.

(geology) A material property (e.g., for rocks or soil) that describes the rate which water can flow through pore spaces or fractures. SI units: m/s. Symbol: K.

A hydraulic ram.

plural of hydram

plural of hydramide

(organic chemistry) One of a group of crystalline bodies produced by the action of ammonia on certain aldehydes.

(zoology) An aquatic mite of the genus Hydrachna or of its relatives in Hydrachnidiae or similar groups.

plural of hydrachnid

(organic chemistry) An isomeric variety of lastic acid that breaks down into acrylic acid and water