lavabo

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ceremonial washing of the hands and recitation from the Psalms by the celebrant before the Eucharist in the Roman Catholic and Anglican churches.
• noun A washbowl that is attached to a wall and filled from a water tank fastened above.

from The Century Dictionary.

• noun The psalm in the mass service which the priest recites at the washing of his hands.
• noun Eccles., in the Roman Catholic Church, and in many Anglican churches, the ritual act of washing the celebrant's hands after the offertory and before entering upon the more solemn part of the eucharistic service: so called from the priest's reciting at the time the last part of the 26th psalm, beginning with the sixth verse, “I will wash my hands in innocency,” in Latin, “Lavabo manus meas in innocentia.” In the Greek Church this takes place in the prothesis, before vesting.
• noun In many monasteries of the middle ages, a large stone basin from which the water issued by a number of small orifices around the edge, for the convenient performance of ablutions before religious exercises or meals.
• noun Hence A convenience of similar object and arrangement in some modern schools or institutions; a lavatory.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A washbasin, especially one attached to the wall of a church, and used for the ceremonial washing of the hands of the celebrant before the eucharist

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a basin for washing the hands (`wash-hand basin' is a British expression)