The term "was big on" refers to having a strong interest or inclination towards something. Some antonyms for this phrase could be "was indifferent to," "was uninterested in," "was dispassionate about," or "was apathetic towards." These words indicate a lack of enthusiasm or passion for the subject in question. Other antonyms could include "was hostile to," "was opposed to," or "was unfavourable towards," which suggest an active dislike or opposition to the topic. In contrast, synonyms for "was big on" might include "was enthusiastic about," "was passionate about," or "was devoted to.