Meaning of "modal verb" in Essential American English Dictionary

modal verb

noun us /ˈmoʊ.dəl ˈvɜrb/ (also modal /ˈmoʊ.dəl/)

B1 a verb, for example “can,” “might,” or “must,” that is used before another verb to show that something is possible, necessary, etc.

(Definition of “modal verb” from the Webster's Essential Mini Dictionary © Cambridge University Press)