n. (Crystallog.) 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,
Twinning axis,
Twinning plane