insidious
/ɪnˈsɪdi.əs/ adjective C2- Causing harm in a stealthy, often gradual, manner.
- Intending to entrap; alluring but harmful. · Hansel and Gretel were lured by the witch’s insidious gingerbread house.
From the library
Watson would assure you that these changes of temperature are most insidious."
Similarly insidious is the conditional apology, often manifesting in the familiar refrain expressing sorrow if you were offended.
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