porpoises Get Printable Handwriting Hear It! Say It! Write It! Learn It! Spelling Test Definition plural noun. small marine mammals related to dolphins. they have a round body and are often seen in groups. Example Sentence Porpoises swim in the ocean. More Example Sentences Many porpoises can be seen jumping. Synonyms marine mammals; cetaceans; dolphins Antonyms land animals; birds Hear It! Say It! Write It! porpoises Switch to cursive Start Share with your friends: