The word 'unclench' is a transparent English formation built from native Germanic elements. Its core, 'clench', derives from the Old English clencan, meaning to hold fast or make firm, a verb likely of imitative origin related to the physical act of gripping. The prefix 'un-', one of the most common and productive in English, is added to indicate the reversal of that action. Therefore, the literal morphemic logic is "to reverse the action of gripping tightly," which maps directly to its modern meaning of releasing a tight grip, whether of a fist, jaw, or muscle.

Structure: un (reverse action) + clench (grip tightly) - un: A prefix of Old English origin, meaning "not" or "to reverse an action." In this word, it functions as a reversative prefix. - clench: A verb of Old English origin (from clencan, meaning "to hold fast, make cling"), functioning as the core root meaning to grip or hold tightly.