| Grammar. any of the group of English auxiliary verbs, including can, could, may, might, shall, should, will, would, and must, that are used with the base form of another verb to express distinctions of mood. |
| modal auxiliary n. A verb characteristically used with other verbs to express mood or tense. In English, the modal auxiliaries are can, may, must, ought, shall, should, will, and would. Also called modal. |