Tau*tom"er*ism (?), n. [Gr. &?;; &?;, for &?; &?; the same + &?; part.] (Chem.) The condition, quality, or relation of metameric substances, or their respective derivatives, which are more or less interchangeable, according as one form or the other is the more stable. It is a special case of metamerism; thus, the lactam and the lactim compounds exhibit tautomerism.

Tau*tom"er*ism (?), n. [Gr. &?;; &?;, for &?; &?; the same + &?; part.] (Chem.) The condition, quality, or relation of metameric substances, or their respective derivatives, which are more or less interchangeable, according as one form or the other is the more stable. It is a special case of metamerism; thus, the lactam and the lactim compounds exhibit tautomerism.

• (chemistry) a form of isomerism in which a dynamic equilibrium between two isomers exists, such as that between an enol and a ketone.