really (adv.)

early 14c., "actually existing, having physical existence (not imaginary);" mid-15c., "relating to things" (especially property), from Old French reel "real, actual," from Late Latin realis "actual," in Medieval Latin "belonging to the thing itself," from Latin res "property, goods, matter, thing, affair," which de Vaan traces to a PIE *Hreh-i- "wealth, goods," source also of Sanskrit rayim, rayah "property, goods," Avestan raii-i- "wealth."

The meaning "genuine" is recorded from 1550s; the sense of "unaffected, no-nonsense" is from 1847. Real estate, the exact term, "land, including what is naturally or artificially on or in it" is recorded from 1660s, but as far back as Middle English real was used in law in reference to immovable property, paired with, and distinguished from, personal. The noun phrase real time is from early 19c. in logic and philosophy, from 1953 as an adjectival phrase in reference to "the actual time during which an event or process occurs," with the rise of computer processes. Get real, usually an interjection, was U.S. college slang in 1960s, reaching wide popularity c. 1987. As a noun, the real, "that which actually exists," by 1818 (Coleridge). The real thing "the genuine article" is by 1818.

Real applies to that which certainly exists, as opposed to that which is imaginary or feigned : as, real cause for alarm ; a real occurrence ; a real person, and not a ghost or a shadow ; real sorrow. Actual applies to that which is brought to be or to pass, as opposed to that which is possible, probable, conceivable, approximate, estimated, or guessed at. [Century Dictionary]

Generally, by the time you are Real, most of your hair has been loved off, and your eyes drop out and you get loose in the joints and very shabby. But these things don't matter at all, because once you are Real you can't be ugly, except to people who don't understand. [Margery Williams, "The Velveteen Rabbit"]

common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).

Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.