nostrum

A medicine whose effectiveness is unproved and whose ingredients are usually secret; a quack remedy.

A favorite but usually ineffective remedy for problems or evils.

A medicine the ingredients of which, and the method of compounding them, are kept secret, for the purpose of restricting the profits of sale to the inventor or proprietor; especially, a quack medicine.

Hence Any scheme or device of a quack or charlatan.

A medicine, the ingredients of which are kept secret for the purpose of restricting the profits of sale to the inventor or proprietor; a quack medicine.