The Collaborative International Dictionary of English v.0.48:

Clear-headed \Clear"-head`ed\ (kl[=e]r"h[e^]d`[e^]d), a.
   Having a clear understanding; quick of perception;
   intelligent. "He was laborious and clear-headed." --Macaulay.
   -- Clear"-head`ed*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

clearheaded
    adj 1: not mentally confused; able to think clearly and act
           intelligently [syn: clearheaded, clear-thinking]
           [ant: confused]