The Collaborative International Dictionary of English v.0.48:

Verb \Verb\, n. [F. verbe, L. verbum a word, verb. See Word.]
   1. A word; a vocable. [Obs.] --South.
      [1913 Webster]

   2. (Gram.) A word which affirms or predicates something of
      some person or thing; a part of speech expressing being,
      action, or the suffering of action.
      [1913 Webster]

   Note: A verb is a word whereby the chief action of the mind
         [the assertion or the denial of a proposition] finds
         expression. --Earle.
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   Active verb, Auxiliary verb, Neuter verb, etc. See
      Active, Auxiliary, Neuter, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

verb
    n 1: the word class that serves as the predicate of a sentence
    2: a content word that denotes an action, occurrence, or state
       of existence