The Collaborative International Dictionary of English v.0.48:

Humbug \Hum"bug`\, n. [Prob. fr. hum to impose on, deceive + bug
   a frightful object.]
   1. An imposition under fair pretenses; something contrived in
      order to deceive and mislead; a trick by cajolery; a hoax.
      [1913 Webster]

   2. A spirit of deception; cajolery; trickishness.
      [1913 Webster]

   3. One who deceives or misleads; a deceitful or trickish
      fellow; an impostor. --Sir J. Stephen.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Humbug \Hum"bug`\, v. t. [imp. & p. p. Humbugged; p. pr. & vb.
   n. Humbugging.]
   To deceive; to impose; to cajole; to hoax.
   [1913 Webster]

WordNet (r) 3.0 (2006):

humbug
    n 1: pretentious or silly talk or writing [syn: baloney,
         boloney, bilgewater, bosh, drool, humbug,
         taradiddle, tarradiddle, tommyrot, tosh, twaddle]
    2: communication (written or spoken) intended to deceive [syn:
       humbug, snake oil]
    3: something intended to deceive; deliberate trickery intended
       to gain an advantage [syn: fraud, fraudulence, dupery,
       hoax, humbug, put-on]
    v 1: trick or deceive