humbug (n.)

1751, student slang, "trick, jest, hoax, imposition, deception," of unknown origin. Also appearing as a verb at the same time, "deceive by false pretext" (trans.). A vogue word of the early 1750s; its origin was a subject of much whimsical speculation even then. "[A]s with other and more recent words of similar introduction, the facts as to its origin appear to have been lost, even before the word became common enough to excite attention" [OED]. Meaning "spirit of deception or imposition; hollowness, sham" is from 1825.