n. In botany: One of the two side petals of a papilionaceous blossom, or the membranous expansion of an organ, as of a fruit, seed, stem, etc. See cut under banner.n. In mosses, one of the basal lobes or auricles of the leaves.n. An axilla or axil.n. In anat., zoöl., etc.:n. A wing.n. Any part of a wing-like or flap-like character: as, ala auris, the upper and outer part of the external ear.n. The armpit.n. plural Specifically, in Cirripedia, the lateral parts of the shell, as distinguished from the parietes, when they are overlapped by others; when they overlap they are termed radii.n. In anc. Rom. arch., a wing or a small apartment placed on each side of the atrium of a Roman house. Audsley.