Scientific truths are tentative. The positive side of theory as 'a guess' is rememberance of that. Often mathematical truths are confounded with scientific ones, for instance in regard of computation and logic.
There's a curious assumption people make that words have a single 'objective' meaning, and that it has always meant that. Words are involved in and affected by social change.
“For a large class of cases of the employment of the word
‘meaning’—though not for all—this word can be explained in this way:
the meaning of a word is its use in the language” -Wittgenstein,
Philosophical Investigations 43
"In this sort of predicament, always ask yourself: How did we learn
the meaning of this word ("good", for instance)? From what sort of
examples? In what language-games? Then it will be easier for you to
see that the word must have a family of meanings." -Wittgenstein, in
Philosophical Investigations 54
In this light, I'm a big fan of going to etymology, so we can catch the development of a word in motion.
Theory (n.) 1590s, "conception, mental scheme," from Late Latin
theoria (Jerome), from Greek theōria "contemplation, speculation; a
looking at, viewing; a sight, show, spectacle, things looked at," from
theōrein "to consider, speculate, look at," from theōros "spectator,"
from thea "a view" (see theater) + horan "to see," which is possibly
from PIE root *wer- (3) "to perceive." Philosophy credits sense
evolution in the Greek word to Pythagoras.
Earlier in this sense was theorical (n.), late 15c. Sense of
"principles or methods of a science or art" (rather than its practice)
is first recorded 1610s (as in music theory, which is the science of
musical composition, apart from practice or performance). Sense of "an
intelligible explanation based on observation and reasoning" is from
It began as a process of reasoning in contemplation of a topic or subject, in Greek thought. With the rise of science, it began to mean a systemisation. Increasingly it has taken on a more specific technical sense of a particular model and it's specific predictions. But that is the most recent development of the term. It's notable that 'theoretical' always means something like 'a guess'.
There are different modes of explanation, and in everyday discourse they may involve unfalsifiable elements. Science has been about progressive constraint on what explanations are considerex good. There just aren't hard boundaries with model and theory, without giving context. I think of Plato's mode of explanation when he related the solar system to musical notes and Platonic Solids, "As the eyes, said I, seem formed for studying astronomy, so do the ears seem formed for harmonious motions: and these seem to be twin sciences to one another, as also the Pythagoreans say" (in The Republic). Consider also reductionism, and What's the "opposite" of emergence?
Kuhn's analysis of paradigms, gets at how there are systems of theories, which constitute the picture of a scientific practice in era by it's practicioners, and that this can change discontinuously. This can be linked to worldview (Which philosophers and philosophies discuss "worldview epistemologies"?) and Foucault's picture of epistemes as the guiding unconsciousness of subjectivity within a given epoch. I mention these, because understanding what commitments a given theory/model/explanation/hypothesis is making, is still in a process of being examined and understood, and changing. In the end, we must relate them to our whole meaning-cosmology (Can the Universe make sense at all?), and so to situating ourselves in the cosmos - and so, to what we ourselves are. You simply cannot 'cut off' a hypothesis or model from who we are, in a deeper sense. It comes down to when you feel a given 'Why?' question has been satisfactorily responded to: "Why ask why" and its scions
I would say then, don't expect words to do the work for you, try to be clear and say what you mean.
"It can scarcely be denied that the supreme goal of all theory is to
make the irreducible basic elements as simple and as few as possible
without having to surrender the adequate representation of a single
datum of experience." -Einstein, in 'On the Method of Theoretical
Which is paraphrased as: State things as simply as possible, but not more simply.