Endless; everlasting; immortal: my undying gratitude. (adjective)
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 "undying" in a sentence
"Employees had agreed to continue working in what they called the undying traditions of professional radio services."
"By the time the spring thaw came, the six of them had formed what the doctor called an undying friendship."
"I will hush ma mouth, especially as he complimented me on my phraseology as I recounted the horror of the unseen tentacles lurking behind the perfect faces of the fur-clad trophy wives who were climbing a hill from which they would call the undying from the deep."