Synonyms for Extrinsic (same or very similar meaning)
WordNet sense 1 (not essential):
extraneousWordNet sense 2 (coming from the outside):
external, outsideWordNet sense 3 (not contained in or deriving from the essential nature of something):
alien, foreignWordNet sense 4 (associated by chance and not an integral part):
accidentalFrom the ODE community, based on WordNetadd/edit