hush-hush

详细解释:n. 机密的
a. 极秘密的
vt. 守秘, 遮盖
【法】 保密, 极保密的事

英语解释：

形容词 hush-hush:

conducted with or marked by hidden aims or methods同义词：clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, secret, surreptitious, undercover, underground