Source : Webster's Revised Unabridged Dictionary (1913)

Preventable \Pre*vent"a*ble\, a.
   Capable of being prevented or hindered; as, preventable
   diseases.

Source : WordNet®

preventable
     adj : capable of being prevented; "conscious of preventable human
           suffering"- A.L.Guerard [ant: {unpreventable}]