copula

from WordNet (r) 3.0 (2006)

copula
    n 1: an equating verb (such as `be' or `become') that links the
         subject with the complement of a sentence [syn: {copula},
         {copulative}, {linking verb}]

from The Collaborative International Dictionary of English v.0.48

Copula \Cop"u*la\, n. [L., bond, band. See {Couple}.]
   1. (Logic & Gram.) The word which unites the subject and
      predicate.
      [1913 Webster]

   2. (Mus.) The stop which connects the manuals, or the manuals
      with the pedals; -- called also {coupler}.
      [1913 Webster]