insidious

word

Definition

Describes something harmful that spreads or develops gradually and secretly, making it hard to detect until it becomes dangerous.

Usage & Nuances

Usually formal, often used to describe diseases, dangers, or problems that appear harmless but become serious over time. Common collocations: 'insidious disease', 'insidious effect'. Not the same as 'sneaky' or 'obvious'.

Example Sentences

Cancer can be an insidious disease.

basic

Stress is insidious—you might not even notice it building up.

natural

It’s the insidious nature of cyber attacks that makes them so dangerous.

natural

The effects of pollution can be insidious.

basic

The virus has an insidious way of spreading.

basic

What’s so insidious about the rumor is how it spread without anyone noticing.

natural