1. A speech form or an expression of a given language that is peculiar to itself grammatically or cannot be understood from the individual meanings of its elements, as in keep tabs on.
2. The specific grammatical, syntactic, and structural character of a given language.
3. Regional speech or dialect.
4. A specialized vocabulary used by a group of people; jargon: legal idiom.
5. A style of artistic expression characteristic of a particular individual, school, period, or medium: the idiom of the French impressionists; the punk rock idiom.
[Late Latin idiōma, idiōmat-, from Greek, from idiousthai, to make one's own, from idios, own, personal, private; see s(w)e- in the Appendix of Indo-European roots.]
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.