Longman Dictionary of Contemporary English
Wiktionary
alt. A container designed to hold small amounts of alcohol, especially spirits, for personal consumption on the go. n. A container designed to hold small amounts of alcohol, especially spirits, for personal consumption on the go.
Wikipedia
Hieronymous "Hip" Flask is a fictional anthropomorphic hippopotamus who appears in comic books published by Active Images and Image Comics. He was created by Richard Starkings.
A hip flask is a thin flask for holding a distilled beverage.
Usage examples of "hip flask".
Hagrid had his usual enormous tankard in front of him, but Moody was drinking from his hip flask.
Barney would have slugged it out with all of them were it not for the fact that he still held the cap to the hip flask in one hand and had to screw it back on so that the tequila in the flask would not be spilled.
As Bram looked on, the woman dredged the needle through the contents of her hip flask, causing a coat of bluish powder to cling to needle and thread.
He must act out his role, feigning a grim resolution he fortified with furtive sips from his hip flask.