"insidious" in the adjective sense
1. insidious
beguiling but harmful
"insidious pleasures"
2. insidious
intended to entrap
3. insidious, pernicious, subtle
working or spreading in a hidden and usually injurious way
"glaucoma is an insidious disease"
"a subtle poison"
Source: WordNet® (An amazing lexical database of English)
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