Unroll comes from un- ('reversal') + roll, from Old French roller, from Vulgar Latin *rotulare, from Latin rotula ('small wheel'), diminutive of rota ('wheel'). In current use it is a verb meaning "to open out something that is rolled up". 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 reversative here, marking an undoing or release rather than mere negation. The surface form is compositional: its joined elements remain visible in the modern word. A diminutive element is part of the history, marking a smaller or derived form. The historical chain includes Old English un- and Latin rota. Related English forms include roll. Derived forms include unrolled and unrolling. As a result, the modern word is best read as a negative, privative, or reversative formation built on a historically older base.