clench

Concise Oxford English Dictionary © 2008 Oxford University Press:
clench/klentʃ/

▶verb

• 1 (with reference to one's fist or teeth) close or press together tightly, in response to stress or anger.

• 2 hold tightly and firmly.

• 3 (of muscles or a muscular part of the body) contract sharply.

▶noun the action of clenching or the state of being clenched.

– derivatives
clenched adjective.

– origin OE (in the sense of clinch ‘fix securely’): of Gmc origin; rel. to cling.