Old English bæð "immersing in water, mud, etc.," also "quantity of water, etc., for bathing," from Proto-Germanic *batham (cf. Old Norse bað, Middle Dutch bat, German bad), from PIE root *bhe- "to warm" (cf. Latin fovere "to foment") + Germanic *-thuz suffix indicating "act, process, condition" (cf. birth, death). Original sense was of heating, not immersing in water. The city in Somerset, England (Old English Baðun) was so called from its hot springs. Bath salts attested from 1875 (Dr. Julius Braun, "On the Curative Effects of Baths and Waters").
n. pl. baths (bāðz, bāths)
The act of soaking or cleansing the body or any of its parts, as in water.
The apparatus used in giving a bath.
The fluid used to maintain the metabolic activities of an organism.
[the third noun sense's dated example refers to a portion of reporter's copy set in type]
a Hebrew liquid measure, the tenth part of an homer (1 Kings 7:26, 38; Ezek. 45:10, 14). It contained 8 gallons 3 quarts of our measure. "Ten acres of vineyard shall yield one bath" (Isa. 5:10) denotes great unproductiveness.