'unresembling' originates from Old English prefix 'un-' (meaning 'not'), combined with 'resemble', specifically the Old French word 'ressembler', where 'res-' is a prefix and 'sembler' relates to Latin 'similis' meaning 'like'.

'unresembling' developed by prefixing Old English 'un-' to Middle English/Old French forms of 'resemble' (from Old French 'ressembler'), and eventually became the modern English present-participial/adjectival form 'unresembling'.

Initially it meant 'not resembling' or 'unlike', and over time it has retained that core sense of 'not like' or 'dissimilar'.