\I`so*mer"ic\, a. [Iso- + Gr. me`ros part: cf. F.
isom['e]rique.] (Chem.)
Having the same percentage composition; -- said of two or
more different substances which contain the same ingredients
in the same proportions by weight, often used with with.
Specif.:
(a) Polymeric; i. e., having the same elements united in the
    same proportion by weight, but with different molecular
    weights; as, acetylene and benzine are isomeric
    (polymeric) with each other in this sense. See
    {Polymeric}.
(b) Metameric; i. e., having the same elements united in the
    same proportions by weight, and with the same molecular
    weight, but which a different structure or arrangement of
    the ultimate parts; as, ethyl alcohol and methyl ether
    are isomeric (metameric) with each other in this sense.
    See {Metameric}.