The underground spring that provides water to a well can be called a wellspring. You can also use wellspring to mean the plentiful source of things like good ideas or information.

If someone comments that you're a wellspring of jokes, they're using the word metaphorically, to mean that jokes seem to pour out of you like water from a spigot. Wellspring comes from the Old English welspryng, which had the literal "spring" meaning. When it's used figuratively, wellspring implies an infinite amount of something: "My dog is a wellspring of affection and stinky breath."

Definitions of wellspring

n the source of water for a well

Type of:
beginning, origin, root, rootage, source
the place where something begins, where it springs into being

n an abundant source

fountainhead, well
Type of:
a document (or organization) from which information is obtained

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