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.
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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.
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 endgame is undefined and unknown, and the bombing of energy and water infrastructure could have high costs for the population, complicating a political transition.
From MarketWatch ● Mar. 10, 2026
“Vladimir” began shooting in July 2025 in Toronto, which stood in for an undefined liberal arts college town.
From Los Angeles Times ● Feb. 26, 2026
Without that definition, the structure of the model lacks formal grounding: Without a defined neutral axis, the construction is formally undefined.
From Science Daily ● Feb. 23, 2026
Jamison was aware that his usual audience, milling outside the property, observed him with undefined expectations.
From "The Underground Railroad: A Novel" by Colson Whitehead
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.
