cloak and dagger

/ˌkloʊk ən ˈdæɡər/
adjective
  1. Involving or characteristic of secret operations, espionage, or intrigue.
    • He loved the cloak-and-dagger world of intelligence work.
    • Their meeting had a cloak-and-dagger atmosphere, with whispered conversations and coded messages.
    • The novel is a thrilling cloak-and-dagger story about spies in World War II.
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