Source : Webster's Revised Unabridged Dictionary (1913)

Dirigible \Dir"i*gi*ble\, a.
   Capable of being directed; steerable; as, a dirigible
   balloon.

Source : WordNet®

dirigible
     adj : capable of being steered or directed [syn: {steerable}]
     n : a steerable self-propelled airship [syn: {airship}]