The word 'unscrew' is a transparent compound formed within English by combining the native Germanic reversative prefix 'un-' with the verb 'screw'. The prefix 'un-' derives from the Proto-Germanic un-, a particle used for negation and reversal, which has a prolific history in forming English verbs that denote undoing (e.g., untie, unlock). The base word 'screw' entered English via Old French 'escroe' (nut, cylindrical socket), which itself evolved from the Latin 'scrofa', meaning a sow. The semantic shift from 'sow' to 'screw' is thought to be metaphorical, comparing the helical thread of a screw to the spiraling tail of a pig. Therefore, 'unscrew' literally means "to reverse the action of screwing," a logical and mechanical formation that perfectly captures its modern meaning of loosening or removing by turning.

Structure: un (reverse action) + screw (fasten with a threaded device) - un: A prefix of Germanic (Old English) origin, meaning "not" or "the opposite of an action". In this word, it functions as a reversative prefix, indicating the undoing of an action. - screw: A noun/verb of Old French ('escroe') and ultimately Latin ('scrofa') origin, referring to a cylindrical fastener with a helical ridge. In this word, it functions as the base verb meaning to fasten or tighten with such a device.