I`so*mer"ic (-m&ebreve;r"&ibreve;k), a. [Iso- + Gr. me`ros part: cf. F. isomérique.] (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 with 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.

• (chemistry) being a isomer
  
• (chemistry) exhibiting isomerism