Green’s Dictionary of Slang

proper adj.

[SE 14C–17C]

1. [mid-16C+] a general intensifier, e.g. a proper idiot.

2. [mid-19C+] correct, first-rate, satisfactory, often used ironically.

In compounds

proper crowd (n.) (also proper bunch, ...mob)

[late 19C+] (Aus.) a circle of like-minded intimates; one’s best friends.