insidious
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Learner's definition of INSIDIOUS
[more insidious; most insidious]formal
: causing harm in a way that is gradual or not easily noticed
- Most people with this insidious disease have no idea that they are infected.
- an insidious enemy
— insidiously
adverb- The disease progresses insidiously.
— insidiousness
noun,[noncount]Comments & Questions
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