noun Date: circa 1904 an auxiliary verb (as can, must, might, may ) that is characteristically used with a verb of predication and expresses a modal modification and that in English differs formally from other verbs in lacking -s and -ing forms
MODAL AUXILIARY
Meaning of MODAL AUXILIARY in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012