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English definition of “insidious”

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insidious

adjective uk   /ɪnˈsɪd.i.əs/ us  
(of something unpleasant or dangerous) gradually and secretly causing harm: High blood pressure is an insidious condition which has few symptoms.
insidiously
adverb uk   /-li/ us  
The disease begins insidiously and progresses relentlessly.
insidiousness
noun [U] uk   /-nəs/ us  
We must recognise the insidiousness of these racial stereotypes.
(Definition of insidious from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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