Does "within" have an antonym? If so, what?

Solution 1:

Mehper beats me to it with outside, so I'll just throw in a third alternative for the sake of completeness. Historically, without is an antonym of within, and Merriam-Webster still says that the first meaning of without is "outside" without further comment, but I don't actually see it being used that way these days. Wiktionary marks that usage as "archaic or literary".

Solution 2:

Outside is an antonym to within.

For example: Within or outside of an organization or institution.

Solution 3:

Outwith means outside of something.

Solution 4:

In Scottish English the antonym is outwith. I think it nicely resolves the problems with using without or outside, which often don't accurately reflect the intended meaning.

There's a picture of it on Wikipedia being used on a sign:

Solution 5:

I agree with "without." Reminds me of a Marx Brothers exchange:

"Without" is a broader term, covering both "lacking" and "the absence of," and also means "outside."

(This double meaning led to the Marx Brothers routine: "There's a girl waiting without." "Without what?" "Without food or clothing." "Well, feed her and send her in.")

From On Language, by William Safire.