insidious

definition: 
Proceeding in a gradual, subtle way, but with harmful effects
sentence: 
The obstruction and harassment is subtle but insidious and seriously affects the ability of the aid agencies to do their job.
Sexually transmitted diseases can be insidious and sometimes without symptoms
difficulty: 
medium
toefl frequency: 
2
toefl classification: 
adverb: 
adjective: 
adverb sentence: 
adjective sentence: 
verb: 
verb sentence: