Carboxyl \Car*box"yl\ (k[aum]r*b[o^]ks"[i^]l), 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}.
[1913 Webster]