Learn English – What term means “one who enjoys learning”

I haven't been able to find a single word that positively describes someone willing to correct others in conversation, but meticulous is a good adjective for someone who cares about details and correctness.

You could combine it with a noun describing what the person is particularly knowledgeable about, e.g. a meticulous grammarian or a meticulous fact-checker.

I think you are referring to the phenomenon of semantic drift, a change in meaning of a word over the course of time.

In the particular examples you describe the semantic change would take the form of semantic broadening or generalization. This is of course the commonest type of change. So your blank could be filled with broadened or generalized.

There is a wikipedia article which lists the various types of semantic change. In a more convenient form I think the changes can be considered under the following categories:

Generalization

Narrowing

Degeneration/Pejoration

Amelioration/Elevation

Hyperbole

Metaphor

Metonymy

Synechdoche