Insidious

/ɪnˈsɪd.i.əs/

Meaning & Definition

adjective

Intended to deceive or entrap; sly, treacherous.

The insidious nature of the disease often means that symptoms do not appear until it is too late for effective treatment.

Having a gradual and cumulative effect; subtle but harmful.

The insidious influence of advertising can manipulate our desires without us even realizing it.

Proceeding in a gradual, subtle way, but with harmful effects.

His insidious plan to undermine the team's efforts went unnoticed until it was too late.

Late Middle English, from Latin 'insidiosus' meaning 'deceitful'.

insidious plot

A scheme that is intended to deceive or betray.

insidious disease

An illness that develops gradually and may not show symptoms until it is advanced.

insidiously

In a way that is deceitful or treacherous.

insidiousness

The quality of being insidious.

Sly or underhanded dealings.

They pulled an insidious move to get ahead in the competition.