1. Not suited to circumstances or needs; unsuitable: improper shoes for a hike; improper medical treatment.
2. Not in keeping with conventional mores; indecorous: improper behavior; an improper suggestion. See Synonyms at unseemly.
3. Not consistent with established truth, fact, or rule; incorrect: improper grammar; an improper conclusion.
4. Irregular or abnormal: complications due to improper functioning of the immune system.
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.