clench (v.) Look up clench at Dictionary.com
Old English (be)clencan "to hold fast, make cling," causative of clingan (see cling); compare stench/stink. Related: Clenched; clenching.
clench (n.) Look up clench at Dictionary.com
"part of a nail that clinchers," 1590s, from clench (v.). Meaning "a grasp, grip" is from 1779.