'self-locking' originates from Modern English, specifically a compound of the words 'self' and 'lock', where 'self' meant 'oneself' and 'lock' meant 'a device for fastening or securing something.'

'self' comes from Old English 'self' (meaning 'oneself'), and 'lock' comes from Old English 'locc' (later Middle English forms such as 'lokk'/'lokken'); the compound 'self-locking' developed in technical and engineering usage in Modern English (19th–20th century) to describe mechanisms that lock by themselves.

Initially the component words meant 'one's own' and 'a fastening device'; over time the compound came to be used specifically in technical contexts to mean 'locking without an external locking action' (the core meaning has remained descriptive of automatic/self-acting locking).