The Collaborative International Dictionary of English v.0.48:

Externalize \Ex*ter"nal*ize\, v. t.
   To make external; to manifest by outward form.
   [1913 Webster]

         Thought externalizes itself in language. --Soyce.
   [1913 Webster]

WordNet (r) 3.0 (2006):

externalize
    v 1: regard as objective [syn: project, externalize,
         externalise]
    2: make external or objective, or give reality to; "language
       externalizes our thoughts" [syn: exteriorize,
       exteriorise, externalize, externalise, objectify]