Unyielding in severity or strictness; unrelenting: relentless persecution. (adjective)
Steady and persistent; unremitting: the relentless beat of the drums. (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 "relentless" in a sentence
"Mr. Christie's aides say the governor hasn't budged from his months-long insistence that he won't enter the presidential fray, despite what one described as a "relentless" stream of calls over the last week from prominent Republicans urging him to run."
"This is what I call the relentless rules of humble arithmetic from Justice Brandeis."
"Those aren't students fighting, but that is a student on top of Berry in what she calls a relentless beating all caught on a cell phone camera."