clench /klentʃ/ BrE AmE verb [transitive]
[ Language: Old English ; Origin: beclencan ]
1 . clench your fists/teeth/jaw etc to hold your hands, teeth etc together tightly, usually because you feel angry or determined:
Jody was pacing the sidelines, her fists clenched.
2 . to hold something tightly in your hand or between your teeth:
a cigar clenched between his teeth