lavatory (n.) Look up lavatory at Dictionary.com
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.