on·set (ŏnsĕt′, ôn-)
1. The beginning or start of something: the onset of a cold.
2. Linguistics The part of a syllable that precedes the nucleus. In the word nucleus (nklē-əs), the onset of the first syllable is (n), the onset of the second syllable is (kl), and the last syllable has no onset.
3. Archaic An attack by military forces; an assault.
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.