Intraloper, weirdly enough, is a word in use.
I'm exter mad about that.
In any single sentence context they cannot refer to the same relationships, and that which they are not is precisely the domain of the other word: they are true antonyms.
External relationships are a thing, which are in neither of those domains.
An intramural activity is not the same thing as an intermural activity, but the overwhelming majority of activities which are not intramural activities are not intermural activities either, most are extramural activities.
They are a subset of inter-, pretty obviously.
Edit: Geometrically, I agree an extraloper could run on secants (or radii) but they're not allowed to strike a chord.
But getting back to generative text, I feel that "tangent" is more appropriate ;-)