'unfoliated' originates from English, specifically formed by the prefix 'un-' + the adjective 'foliated', where the element 'foli-' comes from Latin 'folium' meaning 'leaf'.

'foliate' comes from Latin 'foliatus' (past participle related to 'folium') through Medieval/Old French and Middle English into Modern English 'foliate'; the negated adjective 'unfoliated' is formed in modern English by adding the productive negative prefix 'un-' to 'foliated'.

Originally, 'foliate' meant 'provided with leaves' (or 'leaf-shaped'); the sense broadened to mean 'having leaf-like layers or laminations' (for example in geology); 'unfoliated' developed as the straightforward negative meaning 'lacking those leaves or layers'.