an equating verb (such as `be' or `become') that links the subject with the complement of a sentence
A word, usually a verb, used to link the subject of a sentence with a predicate (usually a subject complement or an adverbial), that unites or associates the subject with the predicate.
The word copula comes from the Latin term meaning "connection" or "linking of words." It is formed by combining the prefix for "together" with a root meaning "to fasten," and it shares a common origin with the English word couple.