carbamic : Idioms & Phrases

• noun an acid that is known only by virtue of its salts (as ammonium carbamate) or its esters (as urethane)
  

WordNet

• (Chem.), an amido acid, NH2.CO2H, not existing in the free state, but occurring as a salt of ammonium in commercial ammonium carbonate; called also amido formic acid.

Webster 1913