reservoir

noun

res·​er·​voir ˈre-zə-ˌvwär  -zər-  -ˌvwȯr 

also -ˌvȯi

1

: a place where something is kept in store: such as

a

: an artificial lake where water is collected and kept in quantity for use

b

: a part of an apparatus in which a liquid is held

c

: supply, store

a large reservoir of educated people

2

: an extra supply : reserve

3

a

: a host organism in which an infectious agent (such as a bacterium or virus) that is pathogenic for some other species lives and multiplies typically without damaging the host

Note: A reservoir serves as a source from which transmission of infection and outbreaks of disease can occur.

Wild rodents also constitute a reservoir of hantaviruses. The viruses are shed in urine, droppings, and saliva, and humans are mainly infected … by inhaling aerosols containing the virus.

—Hilde Kruse et al.

It is the white-footed mouse that serves as a natural reservoir host for the spirochete B. [Borrelia] burgdorferi. These mice carry the spirochete without any apparent harm to themselves, and it is through feeding on infected mice that the immature stages of the tick acquire the spirochete.

—Suzanne Clothier et al.

also : a nonliving thing (such as soil or water) in which an infectious agent lives and multiplies and which serves as a source of infection similar to a host organism

b

: a part of the body that harbors an infectious agent and serves as a source of reinfection or infection transmission

… vulvar or rectal reservoirs, which might increase risk for BV [bacterial vaginosis] recurrence.

—Lisa E. Manhart et al.

compare carrier sense 5a, vector entry 1 sense 2a

Synonyms of reservoir

• supply
• pool
• inventory
• repertoire

Examples of reservoir in a Sentence

The pen has a large ink reservoir.

Colleges and universities provide reservoirs of talent for job recruiters.

She found the reservoirs of energy she needed to finish the job.

Recent Examples on the Web

Because the last three winters in a row have seen above-normal or normal precipitation — the first such streak in 25 years — reservoirs across California began the winter at higher levels than normal. —Paul Rogers, Mercury News, 11 Feb. 2026

Rivers, lakes and reservoirs further north are frozen solid, so the birds fly south to the lower Hudson Valley for open water fishing. —Tony Aiello, CBS News, 11 Feb. 2026

And not everyone is thrilled by the news that otters might be living in the reservoir. —Sophie Hartley, IndyStar, 11 Feb. 2026

The snowpack that builds up over the winter in the Sierra Nevada slowly melts to feed rivers and reservoirs through the spring and summer. —Monica Garske, USA Today, 10 Feb. 2026

Word History

Etymology

French réservoir, from Middle French, from reserver

First Known Use

1690, in the meaning defined at sense 1

Rhymes for reservoir

• abattoir
• alcazar
• autocar
• avatar
• belshazzar
• caviar
• caviare
• cinnabar
• commissar
• condylar
• deodar
• handlebar

Kids Definition

reservoir

noun

res·​er·​voir ˈrez-ə(r)v-ˌwär  -ə(r)v-ˌ(w)ȯr 

1

: a place where something is kept in store

especially : an artificial or natural lake where water is collected as a water supply

2

: an extra supply : reserve

3

: a living thing (as a fly or mouse) in which a parasite (as a bacterium) that is harmful to some other living thing lives and multiplies

Etymology

from French réservoir "place where something is kept in reserve," from reserver "to reserve, keep for future use"

Medical Definition

reservoir

noun

res·​er·​voir ˈrez-ə(r)v-ˌwär  -ə(r)v-ˌ(w)ȯr 

1

: a space (as an enlargement of a vessel or the cavity of a glandular acinus) in which a body fluid is stored

2

a

: a host organism in which an infectious agent (as a bacterium or virus) that is pathogenic for some other species lives and multiplies typically without damaging the host

Note: A reservoir serves as a source from which transmission of infection and outbreaks of disease can occur.

Wild rodents also constitute a reservoir of hantaviruses. The viruses are shed in urine, droppings, and saliva, and humans are mainly infected aerogenically by inhaling aerosols containing the virus.

—Hilde Kruse et al., Emerging Infectious Diseases

also : a nonliving thing (as soil or water) in which an infectious agent lives and multiplies and which serves as a source of infection similar to a host organism

b

: a part of the body that harbors an infectious agent and serves as a source of reinfection or infection transmission

… vulvar or rectal reservoirs, which might increase risk for BV [bacterial vaginosis] recurrence.

—Lisa E. Manhart et al., Infectious Diseases in Obstetrics and Gynecology

carrier sense 1a, vector entry 1 sense 2