'foreignism' originates from English, specifically the adjective 'foreign' (ultimately from Old French 'forain' and Latin 'foraneus') combined with the noun-forming suffix '-ism' (from Greek '-ismos' via Latin '-ismus'), where 'foraneus' meant 'from outside' and '-ismos' denoted a state, practice, or characteristic.

'foreign' changed from Old French 'forain' into Middle English forms such as 'forayn' and eventually became modern English 'foreign'; the suffix '-ism' passed from Greek into Latin and Old French before becoming a productive suffix in Modern English to form nouns (e.g. indicating doctrines, states, or characteristic). Combined as 'foreignism', the word formed in Modern English to denote either a foreign-derived word/usage or the state of being foreign.

Initially, the elements meant 'from outside' (foraneus) and a noun-forming notion of state or practice ('-ism'); over time the combined word 'foreignism' has been used both for concrete foreign-derived words/expressions and for the abstract idea of foreignness, a dual sense that persists today.