afire

adjective

1. on fire: to set a house afire.
2. aflame(def 2).

adverb, adjective (postpositive)

1. on fire; ablaze
2. intensely interested or passionatehe was afire with enthusiasm for the new plan

adj.

c.1200, afure, from a- “on” (see a- (1)) + fire (n.). Figurative use by late 14c.