'unmoor' originates from Old English elements: the prefix 'un-' (Old English 'un-', meaning 'not' or 'reverse') combined with 'moor', from Old English 'mōrian' (to moor), where 'mōr' was related to moorland.

'unmoor' was formed by adding the negative/reversing prefix 'un-' to Old English/Middle English forms of the verb 'moor' (Old English 'mōrian' → Middle English 'moren'/'more'), eventually becoming the modern English 'unmoor'.

Initially it had a literal nautical meaning 'to free a vessel from its moorings'; over time it has also developed figurative senses of 'detaching' or 'destabilizing' someone or something from a fixed position.