The Collaborative International Dictionary of English v.0.48:

Ambitionless \Am*bi"tion*less\, a.
   Devoid of ambition. --Pollok.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ambitionless
    adj 1: having little desire for success or achievement [syn:
           unambitious, ambitionless] [ant: ambitious]