Sentence:  Etorphine, a morphine analog, is a powerful stimulant known as "<WSD>elephant juice</WSD>" because it is used to tranquilize large circus animals. Given in small dosage, it acts as a stimulant. "It ranges up to 10,000 times more powerful than morphine," the New York Daily News quoted one expert as saying. "If there is one drug that does not belong in the body of the thoroughbred it is etorphine. Even a slight overdose could kill a horse." 
Meaning of the word marked with <WSD> tags:  Used as a stimulant for horses.