Any deed characterized by secrecy and concealment; mainly for subversion or deception purposes.
Dated back to the 1560’s, clandestine stems from the Latin clandestinus meaning secret or hidden. This one is derived from the adverbial base celare meaning to hide. It is also related to Latin intestinus, meaning internal.
Why this word?
Say it. CLAN-des-tin. Those three syllables would not work with rapid speech, nor would they work with raising your voice; these three are so well combined that you have to say it quietly, in an-almost-whisper, to fit with its meaning.
Many things can be done secretly, confidentially or underhandedly, but clandestine has this illicit sense of a conspiracy; the sense of a wrong doing.
How to use clandestine?
Personally I recommend the third-person, past tense use, as a first person use would state your illicit confidential doings. You will be a calmer person without such doings… If you insist though, you can say that your last night’s clandestine meeting went very well. You can also say that the meeting was held clandestinely or that the company’s acquisition was conducted clandestinely to prevent shareholders’ learning of the high price. Here are two you would not like to hear or say: your clandestine behavior makes your innocence hard to believe or she clandestinely snuck out of the house.
Always suspect those who are said to conduct themselves in a clandestine manner!