hush-hush
adjective
[ hʌʃˈhʌʃ ]
• (especially of an official plan or project) highly secret or confidential.
• "a hush-hush research unit"
Similar:
secret,
top secret,
confidential,
strictly confidential,
classified,
restricted,
under wraps,
off the record,
not to be made public,
not to be disclosed,
unrevealed,
undisclosed,
unpublished,
untold,
unknown,
sub rosa,
Opposite:
public,
on the record,
