-merism
noun combining form: possession of (such) an arrangement of or relation among constituent chemical units
    tautomerism

-mer·ism
\_məˌrizəm\ noun combining form
(-s)
Etymology: International Scientific Vocabulary -mer + -ism
1. : possession of a (specified) association of substances in chemical compounds
 < isomerism >
 < tautomerism >
2. [International Scientific Vocabulary mer- (III) + -ism] : possession of (such or so many) parts