reduceyoudaoicibaDictYouDict[reduce 词源字典]
reduce: [14] ‘Lessen, diminish’ is a comparatively recent semantic development for reduce. Its Latin ancestor was certainly not used in that sense. This was redūcere, a compound verb formed from the prefix re- ‘back, again’ and dūcere ‘lead, bring’ (source of English duct, duke, educate, etc). It meant literally ‘bring back’, hence ‘restore’ and also ‘withdraw’.

The original ‘bring back’ made the journey to English, and even survived into the early 17th century (‘reducing often to my memory the conceit of that Roman stoic’, Sir Henry Wotton, Elements of Architecture 1624). The sense ‘lessen, diminish’ seems to be the result of a semantic progression from ‘bring back to a particular condition’ via ‘bring back to order’ and ‘bring to subjection’.
=> duct, duke, educate, introduce, produce, redoubt[reduce etymology, reduce origin, 英语词源]
reduce (v.)youdaoicibaDictYouDict
late 14c., "bring back," from Old French reducer (14c.), from Latin reducere "lead back, bring back," figuratively "restore, replace," from re- "back" (see re-) + ducere "bring, lead" (see duke (n.)). Meaning "bring to an inferior condition" is 1570s; that of "bring to a lower rank" is 1640s (military reduce to ranks is from 1802); that of "subdue by force of arms" is 1610s. Sense of "to lower, diminish, lessen" is from 1787. Related: Reduced; reducing.