'untasselled' originates from the English negative prefix 'un-' (from Old English 'un-') meaning 'not', combined with 'tassel', which originates from Old French 'tassel' meaning 'tuft' or 'ornamental fringe'.

'tassel' entered Middle English from Old French 'tassel' (meaning 'tuft'); the adjective 'tasselled' (having tassels) existed in English, and 'untasselled' was formed by adding the negative prefix 'un-' to produce the meaning 'not tasselled'.

Initially it meant 'not having tassels' and this basic sense has remained stable into modern usage.