Select the most appropriate ANTONYM of the given word.

INSIDIOUS

sincere

The most appropriate antonym of the word "insidious" is sincere.

• Insidious means "proceeding in a gradual, subtle, or stealthy way, especially in order to achieve a harmful or destructive purpose."
• Sincere means "free from pretense or deception; honest."

The other words do not have the opposite meaning of "insidious."

• Treacherous means "betraying trust or confidence in a treacherous way."
• Astute means "having or showing keen insight or discernment."
• Stealthy means "moving or acting in a cautious or surreptitious way, so as to avoid detection."