Unstill comes from un- ('not') + still, from Old English stille ('motionless, quiet'), from Proto-Germanic *stillijaz. In current use it is an adjective meaning "not still; restless or in motion". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The prefix un- is negative or privative, marking the absence, denial, or opposite of the base idea. The surface form is compositional: its joined elements remain visible in the modern word. The historical chain includes Old English un-, Old English stille, and Proto-Germanic *stillijaz. Related English forms include still and stillness. As a result, the modern word is best read as a negative, privative, or reversative formation built on a historically older base.