undefined
Americanadjective
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without fixed limits; indefinite in form, extent, or application.
undefined authority; undefined feelings of sadness.
-
not given meaning or significance, as by a definition; not defined or explained.
an undefined term.
-
Mathematics. having no assigned or determinable value under particular conditions.
Any number divided by zero is undefined.
adjective
Other Word Forms
Etymology
Origin of undefined
First recorded in 1605–15; un- 1 + define ( def. ) + -ed 2 ( def. )
Explanation
If something is undefined it's not clear, such as your undefined vacation plans. You know you want to go somewhere during the third week of August, but you just don't know where. You can tell just by looking at it that undefined means "not defined." But you might be surprised that the root define comes from the Old French word defenir, meaning "to end, terminate, determine." In this case, define carries the meaning of "determine," but in a sense "end" and "terminate" apply as well. When you define something, that's the end of it — no more wondering. So if something is undefined, it's not yet determined.
Vocabulary lists containing undefined
Fish in a Tree
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UCPS 6th Grade Roots List #3
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Means to an End: Fin
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
There is a Honda engine upgrade to come for the next race after the summer break - of undefined size.
From BBC ● Jul. 25, 2026
Resuming SAT would be “the wrong approach to an undefined problem,” she said.
From Los Angeles Times ● Jul. 9, 2026
The bulk of that comes from undefined enterprise applications, which SpaceX said will contribute to $22.7 trillion of the TAM.
From MarketWatch ● Jun. 10, 2026
By determining which media — or “torch,” as they’re called — “amplifies light,” an undefined expression that asks each person to vote based on their values.
From Salon ● May 3, 2026
The river world was all brown and shadowy forms—a universe of nameless undefined matter below the surface.
From "100 Sideways Miles" by Andrew Smith
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
