1. the quality of being harmful in a way that is gradual or not easily noticed

Examples

• The insidiousness of the disease made early detection difficult.
• She was shocked by the insidiousness of his betrayal.
• The insidiousness of online misinformation poses a serious threat to democracy.
• The novel explores the insidiousness of prejudice in small-town life.
• Experts warn about the insidiousness of certain financial scams.
• The insidiousness of the corruption became apparent only after years of investigation.