(1):

(n.) A genus of marine gastropods, including many species of limpets. The shell has the form of a flattened cone. The common European limpet (Patella vulgata) is largely used for food.

(2):

(n.) A kind of apothecium in lichens, which is orbicular, flat, and sessile, and has a special rim not a part of the thallus.

(3):

(n.) A small dish, pan, or vase.

(4):

(n.) The kneepan; the cap of the knee.