Diminuendo (9 February 1985 – 2010) was an American-bred, British-trained Thoroughbred racehorse and broodmare best known for winning two classic races, the Epsom Oaks and the Irish Oaks in 1988. She was one of the best two-year-old fillies of 1987, when she won all four of her races including the Cherry Hinton Stakes and Fillies' Mile. In 1988 she was beaten in her first two races, but won her next four, taking the Musidora Stakes, Epsom Oaks, Irish Oaks and Yorkshire Oaks. She finished second when favourite for the St. Leger Stakes and ended her racing career by finishing unplaced in the Prix de l'Arc de Triomphe, but was rated the best three-year-old filly of the season in Europe. She was then retired to stud, where she had some success as a broodmare.