20 synonyms for controversial such as awkward, arguable, and at issue. Controversial is an adjective, and its antonyms are uncontroversial and anodyne.
Arguable, at issue, awkward, contended, contentious, controvertible, debatable, delicate, difficult, disputable, disputed, emotive, moot, open to discussion/question, problematic, sensitive, tendentious, under discussion, and vexed.