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Webster 1913 Edition

Adj.

Symmetrical.

symmetric ‎(comparative more symmetric, superlative most symmetric)

Symmetrical.
(set theory) Of a relation R on a set S, such that xRy if and only if yRx for all members x and y of S (that is, if the relation holds between any element and a second, it also holds between the second and the first).
"Is a sibling of" is a symmetric relation.
(cryptography) Using the same key (or keys that are trivially related) for both encryption and decryption.

symmetrical — see symmetrical

of a relation R on a set S, such that xRy if and only if yRx for all members x and y of S