The Collaborative International Dictionary of English v.0.48:
Pinna \Pin"na\, n.; pl. Pinn[ae], E. Pinnas. [L., a
(a) A leaflet of a pinnate leaf. See Illust. of Bipinnate
leaf, under Bipinnate.
(b) One of the primary divisions of a decompound leaf.
2. (Zool.) One of the divisions of a pinnate part or organ.
3. [L. pinna, akin to Gr. ?.] (Zool.) 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.
4. (Anat.) The auricle of the ear. See Ear.