1. plumbing fixture consisting of a water basin fixed to a wall or floor and having a drainpipe
2. (technology) a process that acts to absorb or remove energy or a substance from a system;
"the ocean is a sink for carbon dioxide"
3. a depression in the ground communicating with a subterranean passage (especially in limestone) and formed by solution or by collapse of a cavern roof
4. a covered cistern; waste water and sewage flow into it