1. Lying in wait; watching an opportunity to ensnare; treacherous; deceitful; intended to ensnare; working secretly.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• insidous,
• issidious,
• insdious,
• incideous,
• insideous,
• insiduous,
• incidious,
• unsirious,
• insidieous,
• insidiouse,
• isidious,
• insidius,
• insipitus,
• unsidious,
• jnsidious,
• knsidious,
• insidios,
• unstydious,
• casideous,
• incedious

• incautious,
• injudicious,
• insidiously,
• incautiously,
• iniquitously,
• inside out,
• insider,
• inside-out,
• iniquitous,
• in stride,
• inside.

The adjective form of the word "insidious" is "insidious".

The plural form of the word "insidious" is "insidious". The word remains the same in both singular and plural form.

The singular form of the word "insidious" is "insidium". However, it is important to note that "insidium" is not commonly used or recognized. "Insidious" is typically used as both the singular and plural form in common usage.