Hush-hush and Mum

Hush-hush adjective - Not known or meant to be known by the general populace.

Mum and hush-hush are semantically related. In some cases you can use "Mum" instead an adjective phrase "Hush-hush".

Mum adjective - Deliberately refraining from speech.

Hush-hush and mum are semantically related. Sometimes you can use "Hush-hush" instead an adjective "Mum".