1. sth which should be kept quiet/secret
it's all very hush-hush
'Hush' is a word describing the sound you make when you want to remind someone to be quiet, similar to 'shush'. If you want to 'keep something hush-hush', it means you wish for it to remain confidential or secret: "Please keep Janie's surprise party hush-hush. I don't want her to find out." This is an informal expression that can be used in social and professional contexts. Similar expressions include 'keep it quiet', 'don't let the cat out of the bag', and 'keep it on the QT'.