noun
( -s )
Etymology: from gerund of twin (III)
1. : the bearing of twins : production of a pair instead of one
2. : the coupling, association, or comparison of two persons or things
the usual twinning of Homer and Vergil — George Saintsbury
3. : the assemblage of two or more crystals or parts of crystals in nonparallel but rational position with reference to each other — compare : twin 4, secondary twinning