good·bye or good-bye also good-by (gd-bī)
Used to express an acknowledgment of parting.
n. pl. good·byes or good-byes also good-bys
1. An acknowledgment at parting, especially by saying "goodbye."
2. An act of parting or leave-taking: many sad goodbyes.
[Alteration (influenced by good day) of God be with you.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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.