The word 'until' originates from the Old Norse phrase 'und til', meaning 'as far as, up to'. The first element, 'und', is related to Old English 'and-' or 'ond-', meaning 'against, toward, up to', a preposition with Proto-Germanic roots. The second element is the common Germanic preposition 'til', meaning 'to'. Over time in Middle English, these two elements fused into a single compound word, 'until', which inherited the core spatial and temporal sense of 'up to a certain point'. Its function narrowed to primarily express a temporal endpoint or limit, solidifying its modern grammatical roles as both a preposition and a conjunction.

The word 'until' is a simplex form derived from Old English. It is not productively formed from separable morphemes in modern English.