Meaning & use
insidious
Last updated
Meanings
adjectivecomparable
Spreading gradually and quietly, causing harm before it is noticed.
Grammar: Used to describe things like diseases, problems, or plans that develop slowly and secretly; it is almost always negative.
Patterns
- an insidious disease
- insidious effects
- something insidious
The insidious disease spread through the village before anyone realized.
Social media can have an insidious effect on teenagers' self-esteem.
The problem was insidious and grew worse over years.
adjectivecomparable
Intended to trick or harm someone in a secret, gradual way.
Grammar: Describes people or plans that are subtly harmful; less common than the first sense but still used.
Patterns
- an insidious plan
- insidious rumors
He had an insidious plan to take over the company.
The insidious rumors destroyed her reputation slowly.
Word forms
| comparative | more insidious |
|---|---|
| superlative | most insidious |
Common combinations
- insidious disease
- The insidious disease showed no symptoms for years.
- insidious effect
- The insidious effect of the policy was felt decades later.
- insidious nature
- The insidious nature of the problem made it hard to solve.
- insidious form
- The insidious form of corruption went unnoticed.
Synonyms and how they differ
- subtle
- Neutral; means not obvious, but does not necessarily imply harm. 'Insidious' always suggests harm.
- stealthy
- Focuses on secrecy of movement, often for people or animals; 'insidious' is more about gradual harm.
- creeping
- Emphasizes slow, gradual movement, often used for things like inflation or plants; 'insidious' adds the idea of unnoticed harm.
Opposites
Word family
- insidiously adverb
- In an insidious manner; gradually and harmfully.
- insidiousness noun
- The quality of being insidious.
Commonly confused: insidious or invidious? insidious or insidious?
insidious vs invidious
Means likely to cause resentment or envy, as in 'an invidious comparison'; it does not mean secretly harmful.
insidious vs insidious
Not to be confused with 'invidious', which sounds similar but has a different meaning.
Practice
The disease was ______; it spread for years without any symptoms.
Choose one answer.
'Insidious' fits because it describes something that spreads gradually and harmfully without being noticed. 'Sudden' and 'obvious' are opposites, and 'harmless' contradicts the idea of harm.
Make it your own
Write a sentence using “insidious”, then check it and compare it with the examples above.