insidious

Though these words are spelled similarly and both have negative meanings, they are not interchangeable. Insidious, which comes from a Latin word meaning "ambush," means "slowly and subtly harmful": the insidious effects of poverty; The candidate launched an insidious whispering campaign against his opponent.Invidious, which comes from another Latin word meaning "looking at with malice," means "causing another person to feel resentment because of unfair treatment," "feeling envious," and "slighting and discriminatory to another person": A judge should not hold membership of an organization that practices invidious discrimination on the basis of race, sex, religion, or national origin.