Definition of auxiliary verb
: a verb (such as have, be, may, do, shall, will, can, or must) that is used with another verb to show the verb's tense, to form a question, etc.
Word by Word Definitions
: a word that characteristically is the grammatical center of a predicate and expresses an act, occurrence, or mode of being, that in various languages is inflected for agreement with the subject, for tense, for voice, for mood, or for aspect, and that typically has rather full descriptive meaning and characterizing quality but is sometimes nearly devoid of these especially when used as an auxiliary or linking verb
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