diminution (n.)

c. 1300, diminucioun, "extenuation of sin;" late 14c. as "act of diminishing, lessening, or reducing; process of becoming less," from Anglo-French diminuciun, Old French diminucion and directly from Latin diminutionem (nominative diminutio), earlier deminutionem, noun of action from past-participle stem of deminuere "lessen, diminish," from de- "completely" (see de-) + minuere "make small" (from PIE root *mei- (2) "small"). Diminishment (1540s) is now obsolete or rare.