Also, let fall. Utter a word or hint, either casually or inadvertently. For example, He let drop the fact that he'd decided to run for office, or She let fall some bits of gossip about the other teachers. [Late 1500s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
Examples from the Web for let drop
No doubt he himself blew it into clear flame by his let-drop news of Claire's death.Rest Harrow