illegitimate
Americanadjective
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born of parents who are not married to each other; born out of wedlock.
an illegitimate child.
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not legitimate; not sanctioned by law or custom.
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unlawful; illegal.
an illegitimate action.
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irregular; not in good usage.
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Logic. not in accordance with the principles of valid inference.
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Obsolete. (formerly, in London)
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of or relating to stage plays in which musical numbers were inserted because of laws that gave only a few theaters the exclusive right to produce straight dramas.
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acting in or producing such productions.
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noun
verb (used with object)
adjective
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born of parents who were not married to each other at the time of birth; bastard
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forbidden by law; illegal; unlawful
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contrary to logic; incorrectly reasoned
noun
Related Words
See illegal.
Other Word Forms
Etymology
Origin of illegitimate
First recorded in 1530–40; il- 2 + legitimate
Explanation
Something illegitimate is unlawful, or improper. If you're a doctor, even a great doctor, but you were never certified by the medical board, then you're an illegitimate doctor. Illegitimate has the root for "law" in it, and something illegitimate is outside the law or custom. A child not born to married parents is known as an illegitimate child, although so many people are making different choices about how to raise families, that the stigma is dropping away, especially if the child isn't the result of philandering (cheating). In King Lear, Edmund is mad that he's an illegitimate son, because it means he can't inherit the throne.
Vocabulary lists containing illegitimate
Black Like Me
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leg, legis
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leg, legis (law)
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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.
The company says that it is “especially concerned about the use of A.I. to help individual humans or small groups gain unprecedented and illegitimate forms of concentrated power.”
From Slate • Feb. 25, 2026
With around 40% of births in the U.S. illegitimate, it’s easy to identify the problem but not so easy to correct it.
From The Wall Street Journal • Feb. 9, 2026
Viewers eventually learn Sophie’s servitude is forced after her parentage is revealed — she’s the illegitimate daughter of an earl.
From Los Angeles Times • Jan. 29, 2026
Interpol only releases very basic data about illegitimate requests for arrests and since 2018 has not revealed which countries are the subject of complaints and inquiries.
From BBC • Jan. 25, 2026
A bishop of Bath, under the imaginary Edward the First, was considered after due reflection to be an unsuitable man for the Archbishopric, because he had too many illegitimate children—not some, but too many.
From "The Once and Future King" by T. H. White
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.
