WordNet sense 1 (not belonging to that in which it is contained; introduced from an outside source):

foreign

WordNet sense 2 (making impure or corrupt by adding extraneous materials):

adulterant, adulterating

WordNet sense 3 (not pertinent to the matter under consideration):

immaterial, impertinent, orthogonal

WordNet sense 4 (coming from the outside):

external, outside

WordNet sense 5 (not forming an essential part of a thing or arising or originating from the outside):

extrinsic