Keep mum

From Fresh Dictionary

English

Idiom

to keep mum

1. ((idiomatic{{#if:|, {{{2}}}{{#if:|, {{{3}}}{{#if:|, {{{4}}}{{#if:|, {{{5}}}{{#if:|, {{{6}}}{{#if:|, {{{7}}}{{#if:|, {{{8}}}{{#if:|, {{{9}}}}}}}}}}}}}}}}}}})) don't talk; especially keep silent about something that may be sensitive or secret

   "Be like dad, keep mum" (British wartime poster)

Synonyms

• keep shtum
• mom's the word