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The Collaborative International Dictionary
Cointension

Cointension \Co`in*ten"sion\, n. The condition of being of equal in intensity; -- applied to relations; as, 3:6 and 6:12 are relations of cointension.

Cointension . . . is chosen indicate the equality of relations in respect of the contrast between their terms.
--H. Spencer.

Wiktionary
cointension

n. The condition of being of equal in intensity; applied to relations.