controller n.

early 15c., countrollen, "to check the accuracy of, verify; to regulate," from Anglo-French contreroller "exert authority," from Medieval Latin contrarotulus "a counter, register," from Latin contra "against" (see contra) + rotulus, diminutive of rota "wheel" (see roll (n.)). The word apparently comes from a medieval method of checking accounts by a duplicate register.

Un contrerollour qui doit contre roller au tresorere de la garderobe toutz lez receitez. [Household ordinances of Edward II, c. 1310]

Sense of "dominate, direct, exercise control over" is from mid-15c. Related: Controlled; controlling. Control group in scientific experiments is attested from 1952 (from a sense of control attested since 1875).

late 14c., "to enumerate, assign numerals to successively and in order; repeat the numerals in order," also "to reckon among, include," from Old French conter "to count, add up," also "tell a story," from Latin computare "to count, sum up, reckon together," from com "with, together" (see com-) + putare "to reckon," originally "to prune," from PIE root *pau- (2) "to cut, strike, stamp."

Intransitive sense "be of value or worth" is from 1857. Related: Counted; counting. Modern French differentiates compter "to count" and conter "to tell," but they are cognates. To count on "rely or depend upon" is from 1640s. To count against (transitive) "to be to the disadvantage of" is by 1888. To count (someone) in "consider (someone) a participant or supporter" is from 1857; count (someone) out in the opposite sense "leave out of consideration" is from 1854.

c. 1500, a variant of controller, with bad spelling due to influence of unrelated French compte "an account," from Latin computare.