[adjective, noun il-i-jit-uh-mit; verb il-i-jit-uh-meyt]
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  1. born of parents who are not married to each other; born out of wedlock: an illegitimate child.
  2. not legitimate; not sanctioned by law or custom.
  3. unlawful; illegal: an illegitimate action.
  4. irregular; not in good usage.
  5. Logic. not in accordance with the principles of valid inference.
  6. Obsolete. (formerly, in London)
    1. 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.
    2. acting in or producing such productions.
  1. a person recognized or looked upon as illegitimate.
verb (used with object), il·le·git·i·mat·ed, il·le·git·i·mat·ing.
  1. to declare illegitimate.

Origin of illegitimate

First recorded in 1530–40; il-2 + legitimate
Related formsil·le·git·i·mate·ly, adverbil·le·git·i·mate·ness, il·le·git·i·ma·tion, noun

Synonyms for illegitimate

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2, 3. See illegal. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for illegitimate

Contemporary Examples of illegitimate

Historical Examples of illegitimate

  • Who he is no one exactly knows; some say an illegitimate son of Beckendorff.

    Vivian Grey

    Earl of Beaconsfield, Benjamin Disraeli

  • The fate of illegitimate children who are "farmed out" is still worse.

  • Girls who have illegitimate children often lose their situations and their honor.

  • I am haunted by the thought of that illegitimate child of my husband's.


    Emile Zola

  • The Latin is illegitimate; and he infers that, therefore, the English is the same.

    The Verbalist

    Thomas Embly Osmun, (AKA Alfred Ayres)

British Dictionary definitions for illegitimate


  1. born of parents who were not married to each other at the time of birth; bastard
  2. forbidden by law; illegal; unlawful
  3. contrary to logic; incorrectly reasoned
  1. an illegitimate person; bastard
Derived Formsillegitimacy or illegitimateness, nounillegitimately, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for illegitimate

1530s, "born out of wedlock," formed in English (and replacing earlier illegitime, c.1500), modeled on Latin illegitimus "not legitimate" (see il- + legitimate). Sense of "unauthorized, unwarranted" is from 1640s. Phrase illegitimi non carborundum, usually "translated" as "don't let the bastards grind you down," is fake Latin (by 1965, said to date from c.1939) (Carborundum was a brand of abrasives).

Online Etymology Dictionary, © 2010 Douglas Harper