WordNet Dictionary- [n] causing the leaves of trees and other plants to fall off (as by the use of chemicals)
- [n] the loss of foliage
Webster's 1913 Dictionary\De*fo`li*a"tion\, n. [LL. defoliare, defoliatum, to shed leaves; L. de- + folium leaf: cf. F. d['e]foliation.] The separation of ripened leaves from a branch or stem; the falling or shedding of the leaves.