What is the proper adjective for jack?

There isn't a single, universally accepted proper adjective for "jack." It depends on the context and what you want to describe. Here are some possibilities:

General:

* Jack-like: This is the most straightforward option, but it's not very elegant.

* Jackish: Similar to "jack-like," but slightly more informal.

Specific:

* Jacksonian: This refers to Andrew Jackson, the 7th president of the United States.

* Jack-in-the-box: This refers to the toy.

* Jackdaw: This refers to the bird.

Informal:

* Jacked: This could refer to someone being muscular, or it could be a slang term for being "high."

Creative:

* You could also invent your own descriptive adjective based on a specific characteristic associated with the word "jack."

It's important to consider the context and choose the adjective that best fits your meaning.