lavabo

Etymology

From the Christian ritual, which was traditionally accompanied in Catholicism by a recitation of Psalm 25:6 (Psalm 26:6, in the Hebrew and in most modern translations) which in Latin begins with the word lavābō (“I will wash”). The sense of "room with a toilet" developed under the influence of lavatory and lav.

noun

1. (Christianity) A ritual involving the washing of one's hands at a church's offertory before handling the Eucharist.
2. (Christianity) The small towel used to dry the priest's hands following the ritual.
   These small liturgical towels got […] the name of Lavabo cloths or Lavaboes. 1870, Daniel Rock, Textile Fabrics, page 203
3. A washbasin, particularly (Christianity) the one in a church used in the ritual.
   […] the […] pontiff, as he […] moved his hands […] at the Lavabo, or at the various benedictions […] 1885, Walter Horatio Peter, Marius the Epicurean, Bk. iv, Ch. xxiii
4. (architecture) A trough used for washing at some medieval monasteries.
5. (humorous, euphemistic) A lavatory: a room used for urination and defecation.
   Mr. Pond fussed out and she heard the door of the little lavabo in the passage open with a loud creak. 1930, Dorothy L. Sayers, chapter XIV, in Strong Poision, page 177