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insidious

/ɪnˈsɪdi.əs/adjective

Causing damage slowly and secretly, so that it goes unnoticed at first.

Example sentences

  • “Rust is insidious, quietly eating away at the frame for years.”
  • “The disease has an insidious onset, with almost no early symptoms.”

Reserved for things that harm gradually: diseases, rumors, prejudice. Do not confuse with 'invidious', which means unfairly discriminatory.

Related words

insightA deep look into the inner workings of something; a clear understanding of it, often used with "into".inscrutableImpossible to understand, read, or interpret.insightfulShowing a deep and clear understanding of something.inscribeTo carve or write words onto a surface or into a book, often as a lasting mark or dedication.insinuateTo suggest something unpleasant in an indirect way instead of saying it outright.insatiableNever satisfied; impossible to fill or fulfill.