insidiously
US /ɪnˈsɪd.i.əs.li/
UK /ɪnˈsɪd.i.əs.li/
副詞
ひそかに, 陰険に, ずる賢く
in a gradual, subtle way, but with harmful effects
例:
•
The disease developed insidiously, showing no obvious symptoms at first.
•
His influence spread insidiously throughout the organization.