The Collaborative International Dictionary of English v.0.48:

Acephalous \A*ceph"a*lous\, a. [See Acephal.]
   [1913 Webster]
   1. Headless.
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   2. (Zool.) Without a distinct head; -- a term applied to
      bivalve mollusks.
      [1913 Webster]

   3. (Bot.) Having the style spring from the base, instead of
      from the apex, as is the case in certain ovaries.
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   4. Without a leader or chief.
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   5. Wanting the beginning.
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            A false or acephalous structure of sentence. --De
                                                  Quincey.
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   6. (Pros.) Deficient at the beginning, as a line of poetry.
      --Brande.
      [1913 Webster]

WordNet (r) 3.0 (2006):

acephalous
    adj 1: lacking a head or a clearly defined head; "acephalous
           worms"

The Devil's Dictionary (1881-1906):

ACEPHALOUS, adj.  In the surprising condition of the Crusader who
absently pulled at his forelock some hours after a Saracen scimitar
had, unconsciously to him, passed through his neck, as related by de
Joinville.