反感 (fǎn gǎn) is a strong, often intellectual or moral disgust or antipathy, used as a noun or adjective. It is more formal and intense than 讨厌 (tǎo yàn 'dislike/annoying'), and less visceral than 恶心 (ě xin 'nauseating/disgusting'). Unlike 嫌 (xián 'to dislike because unsatisfactory'), 反感 does not imply finding fault; it's a deeper emotional aversion.