insidious

adjective

Stress: second syllable

Syllables: in-sid-i-ous (4)

English Definition

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

Example Sentence

The disease has an insidious onset and is difficult to detect.

US IPA /ɪnˈsɪd.i.əs/
UK IPA /ɪnˈsɪd.i.əs/