ad n.

early 15c., "written statement calling attention to (something), public notice" (of anything, but often of a sale); from Old French avertissement (15c., later respelled pedantically as advertissement, a change rejected in French but accepted in English), from stem of avertir "to turn, direct, make aware" (see advertise). Meaning "public notice (usually paid) in a newspaper or other publication," the main modern sense, emerged 1580s and was fully developed by 18c.; later extended to Web sites.

Advertisements are now so numerous that they are very negligently perused, and it is therefore become necessary to gain attention by magnificence of promises and by eloquence sometimes sublime and sometimes pathetick. Promise, large promise, is the soul of an advertisement. I remember a washball that had a quality truly wonderful—it gave an exquisite edge to the razor! ... The trade of advertising is now so near to perfection that it is not easy to propose any improvement. [Johnson, "The Idler," Jan. 20, 1758]

2000 (earlier as the name of a software company), "software that automatically displays or downloads advertising," from ad (n.) + -ware, abstracted from software, etc.