The Collaborative International Dictionary of English v.0.48:

Unfrequent \Un*fre"quent\, a. [Pref. un- not + frequent.]
   Infrequent. --J. H. Newman. -- Un*fre"quent*ly adv.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Unfrequent \Un`fre*quent"\, v. t. [1st pref. un- + frequent.]
   To cease to frequent. [Obs.]
   [1913 Webster]

         They quit their thefts and unfrequent the fields. --J.
                                                  Philips.
   [1913 Webster]