-yl

from The Century Dictionary.

• noun In chem., a suffix commonly used with radicals, denoting the fundamental part, the origin: as, methyl, CH₃, is the fundamental radical of wood alcohol, CH₃OH, methylic ether, (CH₃)₂O, methyl anime, CH₃NH₂, etc.

from the GNU version of the Collaborative International Dictionary of English.

• (Chem.) A suffix used as a characteristic termination of chemical radicals; as in ethyl, carbonyl, hydroxyl, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• suffix organic chemistry A univalent radical or functional group formed from a given molecule. Thus "propyl" from propane, "benzyl" from benzene, and so forth.