Entry 2 senses Webster, 1913 Delphinus · Del·phi·nus · IPA 01 n. A genus of Cetacea, including the dolphin. See Dolphin, 1. 1. A genus of Cetacea, including the dolphin. See Dolphin, 1.(Zool.) See: Dolphin 2. The Dolphin, a constellation near the equator and east of Aquila.(Astron.)