The Collaborative International Dictionary of English v.0.48:

Monobasic \Mon`o*ba"sic\, a. [Mono- + basic.] (Chem.)
   Capable of being neutralized by a univalent base or basic
   radical; having but one acid hydrogen atom to be replaced; --
   said of acids; as, acetic, nitric, and hydrochloric acids are
   monobasic.
   [1913 Webster] monocarbonic