ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ noun
Usage: usually capitalized X
: any of various usually virus diseases of obscure etiology and relationships: as
a. : a viral encephalitis of man first detected in Australia — called also Australian X-disease
b. : blue comb
c. : hyperkeratosis 2b
d. : a serious and widespread virus disease of peaches and related stone fruits characterized by yellowing and shot-holing of the leaves, early defoliation, and loss or mummification of the fruit — called also yellow-red virosis