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Insidious (adverb insidiously)

developing in a very gradual, in a stealthy manner, with the intend of causing damage.

Prostate Cancer is an insidious disease.
by piece September 10, 2006
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The Devil's coochie/vagina. Can also be used as an adjective to describe the temperature of the surrounding climate.
It is insidious in my room.
by SexyTexasPete August 29, 2011
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