SEMI Meaning of SEMI in English [semi] n, pl sem.is [short for semidetached] (1912) chiefly Brit: a semidetached house [2]semi n, pl sem.is (1942): semitrailer [3]semi n, pl sem.is (1942): semifinal--often used in pl. Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012