WordWeb Online

1. Not pertinent to the matter under consideration
   "an issue extraneous to the debate";
   - immaterial, impertinent, orthogonal
    
2. Not essential
   "the ballet struck me as extraneous and somewhat out of keeping with the rest of the play"
    
3. Not belonging to that in which it is contained; introduced from an outside source
   "water free of extraneous matter";
   - foreign
    
4. Coming from the outside
   "extraneous light in the camera spoiled the photograph"; "relying upon an extraneous income";
   - external, outside

See also: adulterant, adulterating, beside the point, extrinsic, irrelevant