'nonisomeric' originates from 'English', specifically the prefix 'non-' + the adjective 'isomeric', where 'non-' meant 'not' and 'isomeric' ultimately derives from Greek elements meaning 'equal' and 'part'.

'isomeric' comes from New Latin/Greek 'isomerēs' (from Greek 'isos' 'equal' + 'meros' 'part'), entered scientific usage in the 19th century as 'isomer'/'isomeric'; the English negative prefix 'non-' was later attached to form 'nonisomeric' to denote the absence of isomeric relationship.

Initially the Greek root related to 'equal parts', and in chemistry 'isomeric' came to describe compounds with the same composition but different arrangement; 'nonisomeric' therefore developed to mean 'not related as isomers' in modern usage.