clench

to close or hold something very tightly

to close or hold something very tightly and with determination

to close or hold something very tightly; 'tight' is used as a flat adverb here

to press two things, typically one's hands or teeth, tightly together

to clench as an automatic physical reaction to fear, pain, or anger

to clench without being aware of the action, often due to stress or while sleeping

to hold an object firmly with one's teeth