Meaning of AUXILIARY in English
in grammar, a helping element, especially a verb or verbal, that adds meaning to the basic meaning of the main verb or verbal in a sentence or verbal phrase. Auxiliaries can convey information about tense, mood, person, and number. An auxiliary verb occurs with a main verb or verbal that is in the form of an infinitive or a participle. English has a rich system of auxiliaries. English auxiliary verbs include the modal verbs, which may express such notions as possibility (may, might, can, could) or necessity (must). In Sam should write to his mother, the modal verb should adds the sense of obligation to the main verb write. Other English auxiliaries are will and shall, which often indicate futurity, and would, which usually indicates desire or intent. Auxiliaries also form the passive voice. Some auxiliary verbs condition an associated change in or addition to the main verb, such as the English expanded form in Mary is washing her hair now, in which the auxiliary verb is occurs with the present participle washing. Another example is the French past indefinite form, as in il a donn and its English equivalent he has given, in which there is not only an independent auxiliary verb (French avoir, English have) but also a change of the main verb to the past participle.
Britannica English vocabulary. Английский словарь Британика. 2012