1. Of the nature of or constituting a portent; foreboding: "The present aspect of society is portentous of great change" (Edward Bellamy).
2. Full of unspecifiable significance; exciting wonder and awe: "Such a portentous and mysterious monster roused all my curiosity" (Herman Melville).
3. Marked by pompousness; pretentiously weighty.
Usage Note: The last syllable of portentous is properly pronounced (-təs). However, under the influence of words like contentious and pretentious, sometimes this word is pronounced (pôr-tĕnshəs), as though it were spelled portentious. Both the (-shəs) pronunciation and the spelling with the i (which is occasionally seen in print) are widely considered to be mistakes.
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.