If someone clarifies a meaning by saying "this is what I mean" and pointing to a dictionary definition, a more appropriate response might be "Oh, I didn't realise that's the way you meant it".

That's a sophisticated response. Though you might care to decide which meaning of "sophisticated" you think I'm referencing here.

(There are, in fact, words with widely varying, and even opposed, definitions. Arguing that someone means one that they clearly don't, in such a case, would be exceedingly uncharitable.)

No, I'm not. Words can have multiple definitions. One definition does not apply, but a different one does. That's how language works. Hell, most adjectives mean more than one thing, that's just English.