PERFIDY Meaning of PERFIDY in English per ‧ fi ‧ dy /ˈpɜːfədi, ˈpɜːfɪdi $ ˈpɜːr-/ BrE AmE noun [uncountable] literary when someone is not loyal to another person who trusts them SYN treachery Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012