bathyoudaoicibaDictYouDict[bath 词源字典]
bath: [OE] Bath is a word widely dispersed among the Germanic languages (German has bad, as does Swedish). Like the others, Old English bæth goes back to a hypothetical Germanic *batham, which perhaps derives from the base *ba- (on the suffix -th see BIRTH). If this is so, it would be an indication (backed up by other derivatives of the same base, such as bake, and cognate words such as Latin fovēre ‘heat’, source of English foment) that the original notion contained in the word was of ‘heat’ rather than ‘washing’.

This is preserved in the steam bath and the Turkish bath. The original verbal derivative was bathe, which goes back to Germanic *bathōn (another derivative of which, Old Norse batha, had a reflexive form bathask, which probably lies behind English bask); use of bath as a verb dates from the 15th century.
=> bask, bathe[bath etymology, bath origin, 英语词源]
bath (n.)youdaoicibaDictYouDict
Old English bæð "immersing in water, mud, etc.," also "quantity of water, etc., for bathing," from Proto-Germanic *batham (cognates: Old Norse bað, Middle Dutch bat, German bad), from PIE root *bhe- "to warm" (see fever) + Germanic *-thuz suffix indicating "act, process, condition" (as in 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").