The Collaborative International Dictionary of English v.0.48:

emotionless \e*mo"tion*less\ adj.
   1. unsusceptible to, destitute of, or showing no emotion;
      unmoved by feeling. Opposite of emotional; as, he kept
      his emotionless objectivity and faith in the cause he
      served. [Narrower terms: matter-of-fact, prosaic;
      philosophical, philosophic; phlegmatic, phlegmatical,
      stolid; stoic, stoical; unblinking] Also See: cool,
      passionless, unmoved(predicate), unmoving.

   Syn: unemotional, passionless.
        [WordNet 1.5]