>Mike's reply seems good enough. But see also the definition at www.dictionary.com. Actually, there are several, for example:
>
>"A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena."
>
>but also:
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>"An assumption based on limited information or knowledge; a conjecture."

Thanks for the above.

I'd always heard that "theory", as a scientific term rather than a 'folk' expression, was: a viable hypothesis with a preponderance of evidence.

So it is a misnomer to say "it's just a theory" in effort to refute or dismiss the science, agreed? Like we would not say "Gravity: a theory, not a fact". Evolution is a central an unifying theory to the whole body of life sciences. That it "can't be proven" really means that we can't convince are those who do not accept it.