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.