Source : Webster's Revised Unabridged Dictionary (1913)

Carboxyl \Car*box"yl\, n. [Carbon + oxygen + -yl.] (Chem.)
   The complex radical, {CO.OH}, regarded as the essential and
   characteristic constituent which all oxygen acids of carbon
   (as formic, acetic, benzoic acids, etc.) have in common; --
   called also {oxatyl}.