The Collaborative International Dictionary of English v.0.48:

Afire \A*fire"\ ([.a]*f[imac]r"), adv. & a. [Pref. a- + fire.]
   On fire.
   [1913 Webster]

WordNet (r) 3.0 (2006):

afire
    adj 1: lighted up by or as by fire or flame; "forests set ablaze
           (or afire) by lightning"; "even the car's tires were
           aflame"; "a night aflare with fireworks"; "candles alight
           on the tables"; "houses on fire" [syn: ablaze(p),
           afire(p), aflame(p), aflare(p), alight(p), on
           fire(p)]