a. Being against established or accepted rules and standards: an illegitimate means of winning a debate.
b. Being against the law; illegal: an illegitimate contract.
c. Not valid or defensible: Their reasons for missing school are illegitimate.
d. Incorrectly deduced; illogical: an illegitimate conclusion.
e. Biology Unacceptable as a scientific name because of not conforming to the international rules of nomenclature.
2. Offensive Born to parents not married to each other.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.