late 14c., "unconditionally, completely," from absolute (adj.) + -ly (2). From mid-15c. as "without reference to anything else, not relatively;" meaning "to the utmost degree" emerged by mid-16c. As a colloquial emphatic, by 1867, American English.
"Cannot something be done in the matter?" I inquired.
"Nothing sir! nothing, absolutely," he said (his family and personal pride evidently rising as he spoke); .... [D.E. Smith, "Leaves from a Physician's Journal," New York: 1867]