insidious
in-SID-ee-uss
/ɪnˈsɪd.i.əs/
Proceeding in a gradual, subtle way, but with harmful or treacherous effects.
Emphasizes stealth, gradual creep, and harmfulness that goes unnoticed until deep damage is done.
The story behind the word. The Romans created insidiae to describe an ambush—literally soldiers who 'sit in' tall grass waiting for prey. Something insidious sits quietly in waiting until it is too late to escape.
Word relationships
- stealthy: Stealthy emphasizes quiet movement, whereas insidious emphasizes gradual, invisible moral or physical harm.
- perfidious: Perfidious emphasizes breach of trust, while insidious emphasizes gradual unseen danger.
- overt: Overt means done openly and plainly evident.
- harmless: Harmless means producing no injury or damage.
Commonly confused with
- invidious: Invidious means likely to arouse resentment, while insidious means subtle and harmful.
Word family
- insidiously (adverb): In an insidious or subtle, harmful manner.
- insidiousness (noun): The quality of being insidious.
Collocations
- insidious disease
- insidious influence
- insidious effect
Idioms & expressions
- snake in the grass
- wolf in sheep's clothing
Example sentences
- "Glaucoma is an insidious disease that causes irreversible vision loss before patients experience any noticeable symptoms." Medical diagnosis
Memory hook
IN-SIT-ious: sits INSIDE quietly until it destroys you. Quiet, gradual ambush.
When not to use
Do not use for sudden, violent, or obvious attacks.
Fun facts
- Widely used in medicine to describe diseases like Alzheimer's or hypertension that develop without early symptoms.
Related words
Explore more words
encroach, imperceptible, subversion, gradual, subvert, incremental
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