Keep Shtum Meaning

(intransitive, colloquial, idiomatic) Don't tell anyone; especially, keep silent about something that may be sensitive or secret.

Example:   If I tell you, you have to promise to keep shtum about it.‎
2012, Kevin Barry, Dark Lies the Island, Random House (ISBN 9781407086149), page 12
  And I would plead that the situation is not unusual. It's just one of those things you're supposed to keep shtum about.