Unhitch is from un- ('reverse') + hitch, a verb of obscure origin first attested in the early modern period, perhaps related to hatch or to a notion of jerking/catching movement. Important recorded forms include un- (Old English). Morphologically, the un- element marks negation, reversal, removal, or deprivation, while the base supplies the action, quality, or state being denied or undone. The wording preserves that uncertainty: the older history is best read as a cautious account rather than a fully settled chain. The modern sense continues the older lexical line without requiring a separate origin. In current use it covers to unfasten or detach from a hitch. The wider family includes derived forms such as unhitched and related words such as hitch.