detailyoudaoicibaDictYouDict[detail 词源字典]
detail: [17] Etymologically, a detail is a ‘little piece cut off’. It comes from French détail, a derivative of détailler ‘cut up’. This was a compound verb formed from the intensive prefix dé- and tailler ‘cut’ (a relative of English tailor and tally). English acquired the word via the French phrase en détail ‘piece by piece, item by item’, source of the central modern meaning ‘individual item, particular’.
=> tailor, tally[detail etymology, detail origin, 英语词源]
detail (n.)youdaoicibaDictYouDict
c. 1600, from French détail, from Old French detail "small piece or quantity," literally "a cutting in pieces," from detaillier "cut in pieces," from de- "entirely" (see de-) + taillier "to cut in pieces" (see tailor).

Modern sense is from French en détail "piece by piece, item by item" (as opposed to en gros), a commercial term used where we would today use retail. Military sense is 1708, from notion of "distribution in detail of the daily orders first given in general," including assignment of specific duties.
detail (v.)youdaoicibaDictYouDict
1630s, from French détailler "cut up in pieces; narrate in particulars," from Old French detaillier, from detail (see detail (n.)). Related: Detailed; detailing.