Used to express an acknowledgment of parting.(interjection)
An acknowledgment at parting, especially by saying "goodbye.”(noun)
An act of parting or leave-taking: many sad goodbyes. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "goodbye" in a sentence
"Drop points here, though, and the Frenchman can kiss the title goodbye on both cheeks."
"The absence of a comma is intentional; the Gunners can kiss the title goodbye"
"In The Cherry Orchard, the goodbye is at first uncertain, but later definite, and for Lyuba, it is a terminal goodbye."