Meaning of complementary distribution

complemen'tary distribu'tion

Pronunciation: [key]
— Ling. Ling.
  1. a relation such that the members of a pair or set of phones, morphs, or other linguistic units have no environment in common, as aspirated “p” and unaspirated “p” in English, the first occurring only in positions where the second does not. Also calledCf. free variation.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.