lavatoryyoudaoicibaDictYouDict[lavatory 词源字典]
lavatory: [14] The notion of ‘washing’ was represented in prehistoric Indo-European by *lou-, which produced Greek loúein ‘wash’, English lather, and Latin lavāre ‘wash’. This last has been a fruitful source of English words, not all of them as obvious as lavatory, which originally meant simply ‘place or vessel for washing’ (its use for a ‘room containing a water closet’ appears to date from the 19th century).

Among its relatives are deluge [14], latrine [17] (from a contraction of Latin lavātrīna), laundry, lava [18] (from Italian lava, which originally denoted a ‘stream caused by sudden rain’), lavish [15] (from the metaphorical notion of an ‘outpouring’), and lotion [14]. And from Latin luere, the form taken on by lavāre after prefixes, we get ablution [14] and dilute [16]. Lavender [15] looks as though it should belong to the same family, but no actual connection has ever been demonstrated.
=> ablution, deluge, dilute, lather, latrine, laundry, lava, lavish, lotion[lavatory etymology, lavatory origin, 英语词源]
lavatory (n.)youdaoicibaDictYouDict
late 14c., "washbasin," from Latin lavatorium "place for washing," noun use of neuter of adjective lavatorius "pertaining to washing," from lavatus, past participle of lavare "to wash" (see lave). Sense of "washroom" is first attested 1650s; as a euphemism for "toilet, W.C.," it is attested by 1864.