Definition of grey dagger in English:

grey dagger

(US gray dagger)

noun

  • A common Eurasian noctuid moth, Acronicta psi, having grey forewings with black dagger-shaped markings, the caterpillar of which is sometimes a pest of fruit trees and ornamental shrubs.

Origin

Mid 18th century; earliest use found in Moses Harris (1730–c1788), entomologist and artist.