Source : Webster's Revised Unabridged Dictionary (1913)

Usnea \Us"ne*a\, n. [NL., from Ar. usnah moss.] (Bot.)
   A genus of lichens, most of the species of which have long,
   gray, pendulous, and finely branched fronds. Usnea barbata is
   the common bearded lichen which grows on branches of trees in
   northern forests.

Usnic \Us"nic\, a. (Chem.)
   Pertaining to, or designating, a complex acid obtained, as a
   yellow crystalline substance, from certain genera of lichens
   ({Usnea}, {Parmelia}, etc.).

Source : WordNet®

Usnea
     n : widely distributed lichens usually having a grayish or
         yellow pendulous freely branched thallus [syn: {genus
         Usnea}]