noun one of the divisions of a pinnate part or organ.
2. pinna ·noun one of the primary divisions of a decompound leaf.
3. pinna ·noun the auricle of the ear. ·see ear.
4. pinna ·noun a leaflet of a pinnate leaf. ·see ·illust. of bipinnate leaf, under bipinnate.
5. pinna ·noun any species of pinna, a genus of large bivalve mollusks found in all warm seas. the byssus consists of a large number of long, silky fibers, which have been used in manufacturing woven fabrics, as a curiosity.