Clandestine means kept secret because it would not be allowed. A clandestine meeting, clandestine operations, clandestine affair.
The would-not-be-allowed part is what distinguishes it from merely private: a clandestine meeting is hidden because it is forbidden. It belongs to intelligence work, to affairs and to resistance movements. In intelligence there is a technical distinction between clandestine, meaning the activity is hidden, and covert, meaning the sponsor is hidden. Note clandestinely.
1adjectiveclandestineKept secret because it would not be allowed.
“The two lovers arranged clandestine meetings in the park.”
synonyms: covert, surreptitious
clandestine is a quality of secrecy.
Latin clandestinus comes from clam, secretly. The word has kept its exact sense for two thousand years, which is unusual.
Proto-Indo-European
*ḱel- (cover)
Latin
clandestīnus — secret, concealed
English, today
clandestine
From Latin clandestīnus (“secret, concealed”); compare French clandestin.
Etymology from Wiktionary, CC BY-SA