Word 'happi' is said to originate from 'hanpi', the sleeveless body wear worn underneath ho (outer robe/vestment), which was put on when sokutai (traditional ceremonial court dress) is worn in ancient time.
「はっぴ」という語は、古代、束帯を着る際に袍（ほう）の下に着用した袖のない胴衣「半臂」（はんぴ）に由来するとされる。