The Collaborative International Dictionary of English v.0.48:

Preen \Preen\, v. t. [imp. & p. p. Preened; p. pr. & vb. n.
   Preening.] [See Preen, n.; or cf. Prune.]
   1. To dress with, or as with, a preen; to trim or dress with
      the beak, as the feathers; -- said of birds. --Derham.
      [1913 Webster]

   2. To trim up, as trees. [Prov. Eng.] --Halliwell.
      [1913 Webster]

   3. Hence: To dress (oneself) carefully or stylishly; to
      primp.
      [PJC]

   4. To pride (oneself) on one's accomplishments; to
      congratulate (oneself).
      [PJC]