'unsheath' is formed in English from the prefix 'un-' (a prefix meaning 'reverse' or 'remove') + 'sheathe' (from Old English elements meaning 'covering for a blade').

'sheathe' comes from Old English (via Middle English) referring to a covering or case for a blade; the compound 'unsheathe' developed in Middle English by adding the prefix 'un-' to 'sheathe', producing the modern verb 'unsheath'.

Initially it meant 'to take (a weapon) out of its sheath,' and over time the sense has remained while also gaining a figurative use meaning 'to reveal' or 'to bring out suddenly.'