parity (n.)

1570s, "equality or equivalence of rank or status," from French parité (14c.) or directly from Late Latin paritas "equality," from Latin adjective par (genitive paris) "equal" (see par (n.)). Meaning "state or condition of being on a level" is from 1610s. Meaning "condition in which adversaries have equal resources" is from 1955, originally in reference to the U.S.A. and the U.S.S.R.