Source : Webster's Revised Unabridged Dictionary (1913)

Copula \Cop"u*la\, n. [L., bond, band. See {Couple}.]
   1. (Logic & Gram.) The word which unites the subject and
      predicate.

   2. (Mus.) The stop which connects the manuals, or the manuals
      with the pedals; -- called also {coupler}.

Source : WordNet®

copula
     n : an equating verb (such as `be' or `become') that links the
         subject with the complement of a sentence [syn: {copulative},
          {linking verb}]
     [also: {copulae} (pl)]