Transvestism is the name for the practice of dressing in the clothes usually worn by the opposite sex — most often used of men wearing women's clothes. It is the abstract noun: the behaviour itself, treated as a topic. 'Transvestism has a long history in the theatre.' A student needs three things here. First, register: this is a formal, rather clinical word, from medical and psychology writing of the last century. Ordinary people say 'cross-dressing', which means the same and sounds neutral and modern. Second, this is about clothes, and it is not the same as being transgender — someone who cross-dresses is usually not asking to live as another sex, and mixing the two up is a common and hurtful mistake. Third, dressing as another sex has been part of theatre, comedy and festival for centuries in many countries, so the word covers everything from a Shakespeare play, where boys played all the women's parts, to a modern drag show — though people in drag today would say 'drag', not this word. As with 'transsexualism', the -ism ending makes it sound like a diagnosis, which is a big reason it has fallen out of use. Read it, understand it, and say 'cross-dressing' yourself.

異裝（穿異性服裝的行為；日常講「變裝」，舊醫學譯「扮異性癖」帶貶義，避免使用）