The Collaborative International Dictionary of English v.0.48:

monocarbonic \mon`o*car*bon"ic\, monocarboxylic
\mon`o*car*box*yl"ic\, a. [Mono- + carbonic.] (Chem.)
   Containing one carboxyl group; as, acetic acid is a
   monocarbonic acid. The more common term is monocarboxylic.
   Contrasted with dicarboxylic, tricarboxylic, etc.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

monocarboxylic
    adj 1: containing one carboxyl group