Real Dictionary

proper
If you say that a way of behaving is proper, you mean that it is considered socially acceptable and right.
The proper thing is the one that is correct or most suitable.
You can add proper after a word to indicate that you are referring to the central and most important part of a place, event, or object and want to distinguish it from other things which are not regarded as being important or central to it.
You use proper to describe things that you consider to be real and satisfactory rather than inadequate in some way.

proper in American English
specially adapted or suitable to a specific purpose or specific conditions; appropriate
adjective: adapted or appropriate to the purpose or circumstances; fit; suitable

proper in British English
adjective: appropriate or suited for some purpose
adverb: (intensifier)