'async' originates from English, specifically as a clipped form of 'asynchronous', where the prefix 'a-' meant 'not' and the element 'synchron-' comes from Greek 'synchronos' meaning 'together (in time)'.

'async' changed from the modern English word 'asynchronous' (itself borrowed from Greek via Latin/Modern English forms) and eventually became the clipped, technical shorthand 'async' widely used in computing and informal speech.

Initially 'asynchronous' meant 'not occurring at the same time'; over time, especially in computing, it acquired the technical sense of 'non-blocking' or 'occurring independently of the main execution thread', and 'async' came to be used as a concise label for that idea.