Definitions:

1. A bottle, flask, or similar vessel having a vacuum between its inner and outer silvered walls, designed to maintain the temperature of its contents. NOUN
   • The vacuum flask's double-walled construction prevents heat from escaping.
2. A container specifically designed to maintain the temperature of its contents, keeping cold items cold and hot items hot for prolonged periods of time. NOUN
   • The silver coating on the interior of the vacuum flask reflect heat back to the flask.
3. An insulated container designed to keep liquids hot or cold for extended periods. NOUN
   • She poured her coffee into a vacuum flask to keep it hot for the entire day.
4. An insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler that the flask's surroundings. NOUN
   • Vacuum flasks have made it possible to transport temperature-sensitive substances over long distances.
5. Flask with double walls separated by vacuum, used to maintain substances at high or low temperatures. NOUN
   • The vacuum flask kept the ice water cold during the long hike.

Synonyms:

• thermos
• thermos bottle
• vacuum bottle