1. Contrary to rule, accepted order, or general practice: irregular hiring practices.
2. Not conforming to legality, moral law, or social convention: an irregular marriage.
3. Not straight, uniform, or symmetrical: irregular facial features.
4. Of uneven rate, occurrence, or duration: an irregular heartbeat.
5. Deviating from a type; atypical.
6. Botany Having differing floral parts, as of a zygomorphic or asymmetric flower.
7. Falling below the manufacturer's standard or usual specifications; imperfect.
8. Grammar Departing from the usual pattern of inflection, derivation, or word formation, as the present forms of the verb be or the plural noun children.
9. Not belonging to a permanent, organized military force: irregular troops.
1. One, such as an item of merchandise, that is irregular.
2. A soldier, such as a guerrilla, who is not a member of a regular military force.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.