Pinna \Pin"na\, n.; pl. Pinn[ae], E. Pinnas. [L., a feather.]

1. (Bot.)
   (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. (Zo["o]l.) One of the divisions of a pinnate part or organ.

3. [L. pinna, akin to Gr. ?.]

(Zo["o]l.) 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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Byssus \Bys"sus\, n.; pl. E. Byssuses; L. Byssi.[L. byssus fine flax, fine linen or cotton, Gr. by`ssos .]

1. A cloth of exceedingly fine texture, used by the ancients. It is disputed whether it was of cotton, linen, or silk. [Written also byss and byssin.]

2. (Zo["o]l.) A tuft of long, tough filaments which are formed in a groove of the foot, and issue from between the valves of certain bivalve mollusks, as the Pinna and Mytilus, by which they attach themselves to rocks, etc.

3. (Bot.) An obsolete name for certain fungi composed of slender threads.

4. Asbestus.

Source: Webster's Revised Unabridged Dictionary (1913)