really

(adverb): In a way or manner that is real, not unreal.
(adverb): (modal) Actually; in fact; in reality.
(adverb): (as an intensifier) Very (modifying an adjective); very much (modifying a verb).
(interjection): Indicating surprise at, or requesting confirmation of, some new information; to express skepticism.
(interjection): (sarcastic, typically exaggerated question.) Indicating that what was just said was obvious and unnecessary; contrived incredulity
(interjection): Indicating affirmation, agreement.
(interjection): Indicating displeasure at another person's behaviour or statement.

"He really is a true friend." / "Really? What makes you so sure?"
But ma, I really, really want to go to the show!
A: He won the Nobel Prize yesterday.
A: I've just been reading Shakespeare - he's one of the best authors like, ever!
A: That girl talks about herself way too much.