Both Uses

hypothesis
in
Midnight in the Garden of Good and Evil
(Edited)

"This is a purely hypothetical question," I said.
p. 350.5 *

hypothetical = imagined (not a real situation)
"Oh, that's right," said Joe, "we were speaking hypothetically, weren't we?"
p. 350.8 *

hypothetically = based on an imagined situation (not a real situation)

Definitions:

(1) (hypothesis as in: a study to test her hypothesis)
a seemingly reasonable, but unproven idea or explanation based upon known facts

In casual conversation, theory is a synonym for hypothesis, but a scientist would say that a hypothesis needs to pass rigorous tests before it could be accepted as a theory.
(2) (hypothesis as in: assume as a working hypothesis)
something that may or may not be true, but is temporarily treated as true to advance a discussion or to further investigation

This sense of hypothesis is typically seen in the form, hypothetical, or hypothetically.
(3) (meaning too rare to warrant focus)