Become or cause to become less serious or gloomy, and more cheerful. For example, Lighten up, Sam—it'll turn out all right. This slangy expression transfers reducing a physical weight to a change of mood or attitude.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use lighten up in a sentence
Doane tweeted, “the film does make fun of Wannabe Berean unimaginative Christians who need to lighten up.”Kirk Cameron Saves Christmas from Abominable Killjoys (Other Christians) | Brandy Zadrozny | November 14, 2014 | THE DAILY BEAST
Jazz lovers who had taken exception to the previous bashing were told to lighten up, and stop complaining.
Of course, I am aware that this is a simply a video game and critics would say I should lighten up.
From Adam Sandler to Tom Lehrer to South Park, a playlist to lighten up the Festival of Lights.Eight Epic Chanukah Songs, From Sandler to ‘South Park’ | Michael Solomon | December 8, 2012 | THE DAILY BEAST
Some partisans undoubtedly thought Eastwood was funny and that the MSM should lighten up.Clint Eastwood Hijacks Mitt Romney’s Moment at the GOP Convention | Howard Kurtz | August 31, 2012 | THE DAILY BEAST
Now at length we were ready; and the countenances of the soldiers began to lighten up a little.Three Years in the Sixth Corps | George T. Stevens
The old gentleman did not lighten up any over the story, as Tom seemed to think he would.Education: How Old The New | James J. Walsh
It was clear and cloudless, the canopy above him, and he knew that ere long the moon would rise and lighten up his surroundings.'19,000' | Burford Delannoy
Difficulties which now seem insurmountable, will gradually disappear; subjects which now seem impenetrable, will soon lighten up.In the School-Room | John S. Hart
Perhaps a "make-up" man was inspired with a glimmer of editorial intelligence to "lighten up" the page.The Scrap Book. Volume 1, No. 2 | Various