a leaflet of a pinnate leaf. see illust. of bipinnate leaf, under bipinnate.-one of the primary divisions of a decompound leaf.-one of the divisions of a pinnate part or organ.-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.-the auricle of the ear. see ear.