The Collaborative International Dictionary of English v.0.48:

Preen \Preen\, n. [AS. pre['o]n a clasp, bodkin; akin to D.
   priem punch, bodkin, awl, G. pfriem, Icel. prj[=o]nn a
   knitting needle, pin, Dan. preen a bodkin, punch.]
   A forked tool used by clothiers in dressing cloth.
   [1913 Webster]

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]

The Collaborative International Dictionary of English v.0.48:

Preen \Preen\, v. i.
   To dress up neatly and smartly; to make oneself well-groomed
   and well-dressed.
   [PJC]

   2. To feel proud of one's achievement; to swell or gloat.
      [PJC]

WordNet (r) 3.0 (2006):

preen
    v 1: clean with one's bill; "The birds preened" [syn: preen,
         plume]
    2: pride or congratulate (oneself) for an achievement [syn:
       preen, congratulate]
    3: dress or groom with elaborate care; "She likes to dress when
       going to the opera" [syn: preen, primp, plume, dress]