The Collaborative International Dictionary of English v.0.48:

Determiner \De*ter"min*er\, n.
   One who, or that which, determines or decides.
   [1913 Webster]

WordNet (r) 3.0 (2006):

determiner
    n 1: an argument that is conclusive [syn: clincher,
         determiner, determining factor]
    2: one of a limited class of noun modifiers that determine the
       referents of noun phrases [syn: determiner,
       determinative]
    3: a determining or causal element or factor; "education is an
       important determinant of one's outlook on life" [syn:
       determinant, determiner, determinative, determining
       factor, causal factor]