A cockleshell is the small, rounded, ridged shell of a cockle, a type of clam that lives in sandy areas near the sea. These shells are easy to recognize because they look like tiny fans with grooves radiating outward from the hinge, usually about the size of a quarter. Beachcombers love finding them because they're often nicely shaped and come in shades of white, cream, and tan.

The word also appears in the famous nursery rhyme “Mary, Mary, Quite Contrary,” where the garden has “silver bells and cockleshells and pretty maids all in a row.” In this case, the cockleshells might refer to the actual shells used as garden decorations, or possibly to flowers that resemble the shells.

Cockleshell can also mean any small, fragile boat. When sailors call a boat a cockleshell, they're usually emphasizing how tiny and vulnerable it seems compared to the vast ocean around it. The phrase cockleshell boat suggests something that looks almost too delicate to survive rough waves, though many small boats are actually quite seaworthy despite their size.