To remain silent; to not say anything; to avoid revealing secret or sensitive information. An alternative spelling of the more common "keep schtum/shtum." It's better to just keep stum when the boss starts flinging accusations than risk further incensing him. We'll need to keep stum about this deal for the time being.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
See also: stum
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.