noun
1.
a. : a plant of the genus Ipomoea (especially I. purpurea ) — see japanese morning glory
b. : a plant of a related genus (as Convolvulus ) — compare field bindweed , hedge bindweed
2. : hooded merganser
3.
a. : someone or something that starts out impressively but fades quickly
was a brilliant student as a freshman, but turned out to be only a morning glory
b. slang : a racehorse that performs well in morning workouts but runs poorly in races