Synonyms for Unfavorable (same or very similar meaning)
WordNet sense 1 (not favorable):
unfavourableWordNet sense 2 (marked by features that oppose constructive treatment or development):
hostileWordNet sense 3 (contrary to your interests or welfare):
adverse, inauspiciousWordNet sense 4 (in an opposing direction):
contrary, contraryFrom the ODE community, based on WordNetadd/edit