sew·er 1 
(sər)
(sər)n.
An artificial, usually underground conduit for carrying off sewage or rainwater.
[Middle English, from Anglo-Norman sewere, from Vulgar Latin *exaquāria : Latin ex-, ex- + Latin aquāria, feminine of aquārius, pertaining to water (from aqua, water; see akw-ā- in the Appendix of Indo-European roots).]