The term 'not trendy' can be expressed in two five-letter words: 'passe' and 'UNHIP'. 'Passe' is a French word meaning 'out of fashion' or 'no longer fashionable'. It is often used to describe something that is no longer popular or relevant. 'UNHIP' is an informal word meaning 'not fashionable' or 'not up-to-date'. It is often used to describe someone or something that is not fashionable or modern. Together, these two words express the idea of something that is not trendy.