hydra

n. [ Hydr- + arachnid. ] (Zool.) An aquatic mite of the genus Hydrachna. The hydrachnids, while young, are parasitic on fresh-water mussels. [ 1913 Webster ]

n. [ Hydr- + acid: cf. F. hydracide. ] (Chem.) An acid containing hydrogen; -- sometimes applied to distinguish acids like hydrochloric, hydrofluoric, and the like, which contain no oxygen, from the oxygen acids or oxacids. See Acid. [ 1913 Webster ]

a. [ Hydr- + acrylic. ] (Chem.) Pertaining to, or designating, an isomeric variety of lactic acid that breaks down into acrylic acid and water. [ 1913 Webster ]

n. [ See Hydra, and Actinia. ] (Zool.) Any species or marine hydroids, of the genus Hydractinia and allied genera. These hydroids form, by their rootstalks, a firm, chitinous coating on shells and stones, and esp. on spiral shells occupied by hermit crabs. See Illust. of Athecata. [ 1913 Webster ]

‖n. [ NL., fr. Gr. "y`dwr water + a"i^ma blood. ] (Med.) An abnormally watery state of the blood; anæmia. [ 1913 Webster ]

a. [ L. hydragogus conveying off water, Gr. &unr_;; "y`dwr water + &unr_; to lead: cf. F. hydragogue.] (Med.) Causing a discharge of water; expelling serum effused into any part of the body, as in dropsy. -- n. A hydragogue medicine, usually a cathartic or diuretic. [1913 Webster]

n. [ Hydr- + -amide. ] (Chem.) One of a group of crystalline bodies produced by the action of ammonia on certain aldehydes. [ 1913 Webster ]

n. [ Hydroxyl + amine. ] (Chem.) One of a series of artificial, organic bases, usually produced as thick viscous liquids by the action of ammonia on ethylene oxide. They have the properties both of alcohol and amines. [ 1913 Webster ]