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]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "preen":
   adorn, array, beautify, bedeck, bedizen, blazon, brush up, clean,
   color, dandify, deck, deck out, decorate, dizen, doll up, dress,
   dress up, embellish, emblazon, embroider, enrich, fettle, fig out,
   fix up, furbish, garnish, grace, groom, gussy up, manicure,
   ornament, paint, pique, plume, prank, prank up, prettify, primp,
   primp up, prink, prink up, redecorate, redo, refurbish, set off,
   set out, smarten, smarten up, spruce up, titivate, trick out,
   trick up, trim