Meaning

adverb to a degree (not used with a negative)

adverb to the greatest extent; completely

adverb of an unusually noticeable or exceptional or remarkable kind (not used with a negative)

originA development of quit, influence by Anglo-Norman quite. Doublet of coy, quit, quiet, and quietus. For an analogous semantic development from the same root, compare Armenian շատ (šat).

Etymology from Wiktionary, CC BY-SA 3.0