Webster's Revised Unabridged Dictionary · 1913

Really

Really (rā"al*lē`) , adverb

Royally. [Obsolete] — Chaucer

Really (rē"al*ly) , adverb

In a real manner; with or in reality; actually; in truth.
Whose anger is really but a short fit of madness. — Swift
Why, really, sixty-five is somewhat old. — Young

Really is often used familiarly as a slight corroboration of an opinion or a declaration.