Word Study
twinning (root: twin)
CIDE DICTIONARY
twinning, n.
The assemblage of two or more crystals, or parts of crystals, in reversed position with reference to each other in accordance with some definite law; also, rarely, in artificial twinning (accomplished for example by pressure), the process by which this reversal is brought about. [1913 Webster]
Polysynthetic twinning, repeated twinning of crystal lamellæ, as that of the triclinic feldspars. -- Repeated twinning, twinning of more than two crystals, or parts of crystals. -- Twinning axis, Twinning plane . See the Note under Twin , n.
For further exploring for "twinning" in Webster Dictionary Online