secret; clandestine; confidential; arcanum;
例句：
1.我的秘密武器一直是我的家庭。
My secret weapon was my family always.
2.許多基督徒是在家里秘密集會(huì)的。
Many christians were meeting secretly in homes.
3.facebook和其他社交網(wǎng)絡(luò)已有數(shù)百萬易受傷害的、秘密的低齡用戶。
Facebook and other social networks already have millions of vulnerable, clandestine underage users.
4.此次暗殺中，27個(gè)秘密特工使用偽造的護(hù)照出行。
The killing involved 27 undercover agents travelling on forged passports.
5.正因如此，一些秘密將繼續(xù)保持下去。
So we are left with something of a mystery.