Source : Webster's Revised Unabridged Dictionary (1913)

Bucket shop \Buck"et shop`\
   An office or a place where facilities are given for betting
   small sums on current prices of stocks, petroleum, etc.
   [Slang, U.S.]

Source : WordNet®

bucket shop
     n 1: an unethical or overly aggressive brokerage firm
     2: (formerly) a cheap saloon selling liquor by the bucket