'undock' is formed in English by prefixing 'un-' (a prefix used to indicate reversal or removal) to 'dock' (the verb meaning 'to place in a dock').

'dock' comes from Middle English 'dok(e)', borrowed from Middle Dutch 'docke' meaning 'a dock or basin' and related Germanic sources; English formed 'undock' by adding the native prefix 'un-' to this verb. The compound sense 'undock' appears in modern nautical usage and later extended to spacecraft and computing.

Initially it meant 'to move a vessel out of a dock' in maritime contexts; over time it has extended to spacecraft (separating spacecraft from a space station) and to electronic/computing contexts (disconnecting devices or undocking interface elements).