n.1 a large natural or artificial lake used as a source of water supply.
2 a any natural or artificial receptacle esp. for or of fluid. b a place where fluid etc. collects.
3 a part of a machine etc. holding fluid.
4 (usu. foll. by of) a reserve or supply esp. of information.
Etymology: F r{eacute}servoir f. r{eacute}server RESERVE