hush up - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Keep from public knowledge, suppress mention of. For example, They tried to hush up the damaging details. [First half of 1600s]