The Collaborative International Dictionary of English v.0.48:

Oxalyl \Ox"a*lyl\, n. [Oxalic + -yl.] (Chem.)
   (a) A hydrocarbon radical (C2O2) regarded as a residue of
       oxalic acid and occurring in derivatives of it.
   (b) An old name for carbonyl.
   (c) An old name for carboxyl.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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]

WordNet (r) 3.0 (2006):

carboxyl
    adj 1: relating to or containing the carboxyl group or carboxyl
           radical [syn: carboxyl, carboxylic]
    n 1: the univalent radical -COOH; present in and characteristic
         of organic acids [syn: carboxyl, carboxyl group]