Breast stroke is a type of swimming style where the swimmer moves their arms and legs simultaneously in a circular motion. However, when considering antonyms for breast stroke, we might think of swimming styles that do not use this circular motion. One possible antonym could be 'freestyle,' which involves a regular alternating arm motion and flutter kicking. Another antonym for breast stroke is 'backstroke,' where swimmers move their arms in a backwards motion while kicking their legs out behind them. Finally, we could also consider 'butterfly stroke' as an antonym, which uses a powerful arm and kicking motion that propels the swimmer through the water in a more dynamic way than the slower, circular motions of breast stroke.