gaper

noun

1. a person or thing that gapes.
2. Also called horse clam. a large clam, Tresus capax, common on gravelly and coarse-sand beaches.

noun

1. a person or thing that gapes
2. any of various large marine bivalve molluscs of the genera Mya and Lutraria that burrow in muddy sand. M. arenaria is the American soft-shelled clam and the two species of Lutraria are the otter shells. The valves have a permanent gap at the hind end

n.

1630s, agent noun from gape (v.). Gaper delay in traffic control parlance attested by 1995.