What is the main idea of the word 'clandestine'?

The word 'clandestine' directly refers to activities that are secretive and concealed, often because they are illicit or not meant to be known by the general public. This term carries a connotation of stealth and hidden motives. The correct understanding of 'clandestine' emphasizes the nature of actions done in secrecy, highlighting the intention to keep something hidden from view or knowledge.

In contrast, the other choices present ideas that entirely oppose the essence of 'clandestine.' Options referring to openness, legality, and being public are unrelated, as they describe qualities that are contrary to the secretive nature that defines the term.