res·er·voir (rĕzər-vwär′, -vwôr′, -vôr′)
1. A natural or artificial pond or lake used for the storage and regulation of water.
2. A receptacle or chamber for storing a fluid.
3. An underground accumulation of petroleum or natural gas.
4. Anatomy See cisterna.
5. A large or extra supply; a reserve: a reservoir of goodwill.
6. Medicine An organism or population that directly or indirectly transmits a pathogen while being virtually immune to its effects.
[French réservoir, from réserver, to reserve, from Old French reserver; see RESERVE.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.