The Collaborative International Dictionary of English v.0.48:

Dope \Dope\, v. t.
   1. To treat or affect with dope; as, to dope nitroglycerin;
      specif.:
      (a) To give stupefying drugs to; to drug. [Slang]
      (b) To administer a stimulant to (a horse) to increase his
          speed. It is a serious offense against the laws of
          racing. [Race-track Slang]
          [Webster 1913 Suppl.]

   2. To judge or guess; to predict the result of, as by the aid
      of dope. [Slang]
      [Webster 1913 Suppl.]

   3. to impregnate with a dopant.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Dope \Dope\ (d[=o]p), n. [D. doop a dipping, fr. doopen to dip.
   Cf. Dip.]
   1. Any thick liquid or pasty preparation, as of opium for
      medicinal purposes, of grease for a lubricant, etc.
      [Webster 1913 Suppl.]

   2. Any preparation, as of opium, used to stupefy or, in the
      case of a race horse, to stimulate. [Slang or Cant]
      [Webster 1913 Suppl.]

   3. An absorbent material; esp., in high explosives, the
      sawdust, infusorial earth, mica, etc., mixed with
      nitroglycerin to make a damp powder (dynamite, etc.) less
      dangerous to transport, and ordinarily explosive only by
      suitable fulminating caps.
      [Webster 1913 Suppl.]

   4. Information concerning the previous performances of race
      horses, or other facts concerning them which may be of
      assistance in judging of their chances of winning future
      races; similar information concerning other sports; by
      extension, any information not generally known, especially
      when coming from an inside source; as, the inside dope.
      [Sporting Slang]
      [Webster 1913 Suppl. +PJC]

   5. an ignorant or stupid person. [Colloq.]
      [PJC]

   get the dope on learn the true story; get the inside
      information.

WordNet (r) 3.0 (2006):

dope
    n 1: street names for marijuana [syn: pot, grass, green
         goddess, dope, weed, gage, sess, sens, smoke,
         skunk, locoweed, Mary Jane]
    2: an ignorant or foolish person [syn: dumbbell, dummy,
       dope, boob, booby, pinhead]
    3: carbonated drink flavored with extract from kola nuts (`dope'
       is a southernism in the United States) [syn: cola, dope]
    4: slang terms for inside information; "is that the straight
       dope?" [syn: dope, poop, the skinny, low-down]
    v 1: take drugs to improve one's athletic performance
    2: add impurities to (a semiconductor) in order to produce or
       modify its properties; "The resistors have been doped"
    3: give a narcotic to; "The athletes were dope by the coach
       before the race" [syn: dope, dope up]