[ adjective, noun il-i-jit-uh-mit; verb il-i-jit-uh-meyt ]

  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.

  1. unlawful; illegal: an illegitimate action.

  2. irregular; not in good usage.

  3. Logic. not in accordance with the principles of valid inference.

  4. Obsolete. (formerly, in London)

    • 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.

    • 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

synonym study For illegitimate

2, 3. See illegal.

Other words from illegitimate

  • il·le·git·i·mate·ly, adverb
  • il·le·git·i·mate·ness, il·le·git·i·ma·tion, noun

Words Nearby illegitimate Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use illegitimate in a sentence

British Dictionary definitions for illegitimate


/ (ˌɪlɪˈdʒɪtɪmɪt) /

  1. born of parents who were not married to each other at the time of birth; bastard

  2. forbidden by law; illegal; unlawful

  1. contrary to logic; incorrectly reasoned

  1. an illegitimate person; bastard

Derived forms of illegitimate

  • illegitimacy or illegitimateness, noun
  • illegitimately, 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