undefined
Americanadjective
-
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.
adjective
Other Word Forms
Derived 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.
Then there’s the matter of those undefined costs for family caregivers.
From MarketWatch • Mar. 4, 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
Even the title is undefined; a direct translation from the German would be “Looking at the Sun,” which switches senses.
From The Wall Street Journal • Jan. 15, 2026
He was not afraid of danger in the open, only of danger undefined and tinged with the supernatural.
From "And Then There Were None" by Agatha Christie
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.
