bathroom (n.)

also bath-room, 1780, from bath + room (n.). Originally a room with apparatus for bathing (the only definition in "Century Dictionary," 1902); it came to be used 20c. in U.S. as a euphemism for a lavatory and often is noted as a word that confuses British travelers. To go to the bathroom, euphemism for "relieve oneself; urinate, defecate," is from 1920 (in a book for children), but typically is used without regard for whether an actual bathroom is involved.