Noun
The word which unites the subject and predicate.
The stop which connects the manuals, or the manuals with the pedals; -- called also coupler.
Source: Webster's dictionaryA copula is often a verb or a verb-like word, though this is not universally the case. citation A verb that is a copula is sometimes called a copulative or copular verb. Source: Internet
Additional uses of copular verbs A copular verb may also have other uses supplementary to or distinct from its uses as a copula. Source: Internet
Another auxiliary-type usage of the copula in English is together with the to-infinitive to denote an obligatory action or expected occurrence: "I am to serve you"; "The manager is to resign". Source: Internet
As noted above under zero copula, Russian and other East Slavic languages generally omit the copula in the present tense. Source: Internet
Another copula is du, which is a verb that means all its arguments are the same thing (equal). Source: Internet
Aristotle further distinguished (a) terms that could be the subject of predication, and (b) terms that could be predicated of others by the use of the copula ("is a"). Source: Internet