Why are check out and check in two words used in source control systems?

This is jargon, but please keep in mind all the words are similar. The first usage I encountered was in RCS, in 1982.

The term check out derives from a hotel or supermarket checkout.

To check out is to obtain your program from the source control system.

To check in is to put your program into the source control system.

The existing word is Orchidist.

From reading some links provided by Google, it seems to be used by Orchid fanciers, and even appears in My 1976 Concise Oxford.

Kitchenware covers everything you would want in a kitchen.

Style

is an expression of appearance, design, clarity or a refinement of manners, dress, etc.

I don’t like his style, although he is usually positive, but it can sometimes

attract negative elements for example. He looks like a banana.

Other terms would be “dress sense”.