properyoudaoicibaDictYouDict[proper 词源字典]
proper: [13] Proper originally meant ‘belonging to itself, particular to itself’ (a sense now defunct in English except in certain fossilized contexts, such as the astronomical term proper motion). It comes via Old French propre from Latin prōprius ‘one’s own’, which may have been a lexicalization of the phrase prō prīvō, literally ‘for the individual’ (prīvus is the source of English private). The word developed widely in meaning in Latin, but its main modern English senses, ‘correct’ and ‘morally right’, are of later evolution. Appropriate [15] goes back to a late Latin derivative.
=> appropriate, property[proper etymology, proper origin, 英语词源]
proper (adj.)youdaoicibaDictYouDict
c. 1300, "adapted to some purpose, fit, apt; commendable, excellent" (sometimes ironic), from Old French propre "own, particular; exact, neat, fitting, appropriate" (11c.), from Latin proprius "one's own, particular to itself," from pro privo "for the individual, in particular," from ablative of privus "one's own, individual" (see private (adj.)) + pro "for" (see pro-). Related: Properly.

From early 14c. as "belonging or pertaining to oneself; individual; intrinsic;" from mid-14c. as "pertaining to a person or thing in particular, special, specific; distinctive, characteristic;" also "what is by the rules, correct, appropriate, acceptable." From early 15c. as "separate, distinct; itself." Meaning "socially appropriate, decent, respectable" is first recorded 1704. Proper name "name belonging to or relating to the person or thing in question," is from late 13c., a sense also preserved in astronomical proper motion (c. 1300). Proper noun is from c. 1500.