noun
1. subtle and cumulative harmfulness (especially of a disease)
• Derivationally related forms: ↑insidious
• Hypernyms: ↑harmfulness, ↑injuriousness
2. the quality of being designed to entrap
• Derivationally related forms: ↑insidious
• Hypernyms: ↑perfidy, ↑perfidiousness, ↑treachery
Useful english dictionary. 2012.