The Collaborative International Dictionary of English v.0.48:

behaviorist \behaviorist\ behavioristic \behavioristic\adj.
   of, pertaining to, or characteristic of behaviorists or
   behaviorism.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

behaviorist \behaviorist\ n.
   a psychologist who subscribes to behaviorism.

   Syn: behaviourist.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

behaviorist
    adj 1: of or relating to behaviorism; "behavioristic psychology"
           [syn: behavioristic, behaviorist, behaviouristic,
           behaviourist]
    n 1: a psychologist who subscribes to behaviorism [syn:
         behaviorist, behaviourist]