What is known as snake oil is usually a combination which is handed out by the dealer to satisfy the demand of some credulous customer. A genuine oil of course is that which is obtained by "trying out" the fat of a snake, usually the rattlesnake, and to preserve their faces druggists sometimes employ a small proportion of such oil in preparing the weird mixtures dispensed by them. ["The Practical Druggist," July 1912]
[snake oil etymology, snake oil origin, 英语词源]