conch / kängk; känch/ • n. (pl. conchs / kängks/ or conches / ˈkänchiz/ ) 1. (also conch shell) a tropical marine mollusk (Strombus and other genera, family Strombidae) with a spiral shell that may bear long projections and have a flared lip. ∎ a shell of this kind blown like a trumpet to produce a musical note, often depicted as played by Tritons and other mythological figures. 2. Archit. the roof of a semicircular apse, shaped like half a dome.