insidious
//ɪnˈsɪd.i.əs//
Adjective
insidiousCanonical form
more insidiousComparative
most insidiousSuperlative
1
Proceeding in a gradual, subtle way, but with harmful effects.
The disease has an insidious onset, making it difficult to detect in its early stages.
2
Treacherous; crafty; operating or proceeding in an inconspicuous or seemingly harmless way but actually with grave effect.
The disease has an insidious onset, often going unnoticed until it becomes severe.