pocket flask

noun1

1. •
   (old-fashioned) A flat metal container for alcoholic beverages, with a narrow neck suitable for use as a drinking spout, designed to fit into a man's pocket and popular in the 19th and early 20th centuries.

   • The traveller had been at the pains of going a long way up stairs to his sleeping-room, to fetch his pocket-flask of brandy. — 1855