'knock-out drops' definitions:

Definition of 'knock-out drops'

From: GCIDE

knockout drops \knockout drops\, knock-out drops \knock-out drops\n. pl. Drops of any drug, used to a person to fall asleep or become unconscious or stupefied for the purpose of robbery, etc.; they are usually mixed into a drink so that the person consuming it does so unknowingly. One compound used for this purpose is chloral hydrate. [Slang, U. S.] [Webster 1913 Suppl. + PJC]