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.
1. n. marijuana. (Drugs.) This stum is cashed. Trash it.
2. Go to stumbles.
See also: stum