The Collaborative International Dictionary of English v.0.48:

Deterrent \De*ter"rent\, a. [L. deterrens, p. pr. of deterrere.
   See Deter.]
   Serving to deter. "The deterrent principle." --E. Davis.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Deterrent \De*ter"rent\, n.
   That which deters or prevents.
   [1913 Webster]

WordNet (r) 3.0 (2006):

deterrent
    adj 1: tending to deter; "the deterrent effects of high prices"
    n 1: something immaterial that interferes with or delays action
         or progress [syn: hindrance, hinderance, deterrent,
         impediment, balk, baulk, check, handicap]