conch (n.) "large sea-shell," originally of bivalves, early 15c., from Latin concha "shellfish, mollusk," from Greek konkhē "mussel, cockle," also metaphoric of shell-like objects ("hollow of the ear; knee-cap; brain-pan; case round a seal; knob of a shield," etc.), from PIE root konkho- (source also of Sanskrit sankha- "mussel") or else from a Pre-Greek word.