under someone's thumb

Controlled or dominated by someone, as in He's been under his mother's thumb for years. The allusion in this metaphoric idiom is unclear, that is, why a thumb rather than a fist or some other anatomic part should symbolize control. [Mid-1700s]

Words nearby under someone's thumb

under one's skin, under pain of, under par, under secretary, under someone's spell, under someone's thumb, under someone's wing, under the aegis of, under the circumstances, under the counter, under the gun