The Collaborative International Dictionary of English v.0.48:

Headpiece \Head"piece`\ (-p[=e]s`), n.
   1. Head.
      [1913 Webster]

            In his headpiece he felt a sore pain. --Spenser.
      [1913 Webster]

   2. A cap of defense; especially, an open one, as
      distinguished from the closed helmet of the Middle Ages.
      [1913 Webster]

   3. Understanding; mental faculty.
      [1913 Webster]

            Eumenes had the best headpiece of all Alexander's
            captains.                             --Prideaux.
      [1913 Webster]

   4. An engraved ornament at the head of a chapter, or of a
      page.
      [1913 Webster]

WordNet (r) 3.0 (2006):

headpiece
    n 1: the band that is the part of a bridle that fits around a
         horse's head [syn: headstall, headpiece]
    2: a protective helmet for the head

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "headpiece":
   Vernunft, bean, brain, brains, brow, cap, capsheaf, caput, chapeau,
   conception, conk, coverchief, crest, crown, discourse of reason,
   discursive reason, dome, esprit, gray matter, handkerchief, hat,
   head, headcloth, headdress, headgear, heading, headtire, headwear,
   intellect, intellection, intellectual faculty, intelligence,
   kerchief, lid, mens, mental capacity, mentality, millinery, mind,
   noddle, noggin, noodle, nous, pate, pinhead, poll, power of reason,
   psyche, ratio, rationality, reason, reasoning, reasoning faculty,
   ridge, sconce, smarts, topknot, understanding