Definition

Something that is harmful in a subtle or sneaky way, often appearing attractive or appealing at first.

Example

The insidious effects of the drug were not immediately apparent.

Conversation

I heard some insidious rumors about the new manager.

Really? What are people saying?

They claim he's hiding some major issues with the project.

That's concerning. I hope it's just gossip and not true.

Synonyms & Antonyms

Root Explanation

Insidious is formed from "in-" (meaning not) and "sidius" (from the Latin "sedere", meaning to sit). The word describes something that sits in wait, often in a deceptive or treacherous manner, hence the connotation of being harmful but not immediately obvious.

Memory Tip

Think of something that is 'not' obvious ('in-') and 'sitting' ('sidius') in wait to cause harm. This helps you remember that insidious refers to something harmful that is hidden or deceptive.

Visually Confused Words