noun
1. blue devils plural : low spirits : despondency , melancholy
2.
a. : a common blue-rayed aster ( Aster lowrieanus ) of the eastern United States
b. : blueweed 1
3.
a. : either of two Australian percoid fishes ( Paraplesiops gigas and P. meleagris ) brightly marked with light blue dots
b. : a small brilliantly marked blue fish ( Pomacentrus fuscus ) of the West Indies