From Longman Dictionary of Contemporary Englishcontroversialcon‧tro‧ver‧sial /ˌkɒntrəˈvɜːʃəl◂ $ ˌkɑːntrəˈvɜːr-/ ●●○AWL adjectiveDISAGREEcausing a lot of disagreement, because many people have strongopinions about the subject being discussedthe controversial issue of welfare reforma highly controversial (=very controversial) plan to flood the valley in order to build a damHe is a controversial figure (=person who does controversial things) in the art world. —controversially adverbCOLLOCATIONSnounsa controversial issue/topic/subjectI tried to avoid controversial topics such as politics and religion.a controversial decisionThe court’s decision was highly controversial.a controversial plan/proposal/policythe controversial plan to build a new airporta controversial figure (=a person who does controversial things)He is a controversial figure in politics.a controversial measure (=an official action that is controversial)Banning smoking in public places was a controversial measure.controversial legislation (=controversial laws)The controversial legislation has not yet been officially approved.the controversial nature of somethingThe report was kept secret because of its controversial nature.adverbshighly controversialThis policy is highly controversial.politically controversialThe area of workers’ rights remains politically controversial.THESAURUScontroversial causing a lot of disagreement and angryargument, especially in the newspapers, on television etcAbortion is a controversial subject.The film was highly controversial at the time.contentious formallikely to cause a lot of disagreement and argument the contentious issue of immigration These claims are highly contentious.debatable/arguable used when you think that something is not certain and that people have different opinions about it, especially in the phraseit is debatable/arguable whetherIt is debatable whether this book is as good as her previous novel. It is arguable whether these measures will reduce the overall cost. Does the treatment work? I think that’s debatable.something is a moot point used when you think that something is not certain and that people have different opinions about it – a rather formal phraseWhether this proposal will really reduce crime is a moot point.