Reduce
late Middle English: from Latin reducere, from re- ‘back, again’ + ducere ‘bring, lead’. The original sense was ‘bring back’ (hence ‘restore’, now surviving in reduce (sense 5)); this led to ‘bring to a different state’, then ‘bring to a simpler or lower state’ (hence reduce (sense 3)); and finally ‘diminish in size or amount’ (reduce (sense 1), dating from the late 18th century).
wiktionary
From Middle English reducen, from Old French reducer, from Latin redūcō(“reduce”); from re-(“back”) + dūcō(“lead”). See duke, and compare with redoubt.
etymonline
reduce (v.)
late 14c., reducen, "bring back" (to a place or state, a sense now obsolete), also "to diminish" (something), from Old French reducer (14c.), from Latin reducere "lead back, bring back," figuratively "restore, replace," from re- "back" (see re-) + ducere "bring, lead" (from PIE root *deuk- "to lead").
In Middle English largely with positive senses, including "bring back to virtue, restore to God; bring back to health." The specific meaning "bring to an inferior condition" is by 1570s; that of "bring to a lower rank" is by 1640s (military reduce to ranks is from 1802); that of "subdue by force of arms" is from 1610s. The sense of "to lower, diminish, lessen" is from 1787. Related: Reduced; reducing.
