FORTISSIMO Meaning of FORTISSIMO in English adj., adv., & n. Mus. adj. performed very loudly. adv. very loudly. n. (pl. -os or fortissimi) a passage to be performed very loudly. [ It., superl. of FORTE(2) ] Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012