hush-hush

hush-hush (comparative more hush-hush, superlative most hush-hush)

1. Secret, not spoken of (or spoken of only in hushed whispers between insiders).

   The spy program was very hush-hush: no-one ever spoke of it.

• See also Thesaurus:covert

hush-hush (uncountable)

1. secrecy; covert operation
   • 1933, The China Monthly Review, volume 67, page 64:

     I find a very definite policy of hush-hush here about what Japan is doing […]