1. 秘密的：clamorous#吵闹的 | clandestine#秘密的 | cogent#强有力的

2. 暗中的,秘密的：clan n. 宗族;部落 | clandestine 暗中的,秘密的 | distort v. 歪曲;扭曲

3. 秘密的,暗中从事的：clandestine 秘密的,暗中从事的 | clothesline 晒衣绳;(俚)私人事情,家丑 | collaborate 协作,合作;协调

4. 秘密的/暧：clan /氏族/部族/一族/一门/党派/派阀/家族/族/ | clandestine /秘密的/暧/ | clandestinely /秘密地/暗中地/

1. (通常因违法而)偷偷摸摸的，暗地里的，秘密的
Something that is clandestine is hidden or kept secret, often because it is illegal.

e.g. ...their clandestine meetings.
他们的秘密会晤

adj

1. conducted with or marked by hidden aims or methods

e.g. clandestine intelligence operations
cloak-and-dagger activities behind enemy lines
hole-and-corner intrigue
secret missions
a secret agent
secret sales of arms
surreptitious mobilization of troops
an undercover investigation
underground resistance

Synonym: cloak-and-daggerhole-and-corner(a)hugger-muggerhush-hushsecretsurreptitiousundercoverunderground