The Collaborative International Dictionary of English v.0.48:

Dimethyl \Di*meth"yl\, n. [Pref. di- + methyl.] (Chem.)
   Ethane; -- sometimes so called because regarded as consisting
   of two methyl radicals. See Ethane.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

ethane \eth"ane\ ([e^]th"[=a]n), n. [From Ether.] (Chem.)
   A gaseous hydrocarbon, C2H6, forming a constituent of
   ordinary illuminating gas. It is the second member of the
   paraffin series, and its most important derivatives are
   common alcohol (ethyl alcohol), acetaldehyde, ether, and
   acetic acid. Called also dimethyl.
   [1913 Webster]