Synonyms for Insidious (same or very similar meaning)
WordNet sense 1 (tending to entice into a desired action or state):
seductive
WordNet sense 2 (involving or causing danger or risk; liable to hurt or harm):
dangerous, unsafe
WordNet sense 3 (working or spreading in a hidden and usually injurious way):
pernicious, subtle
WordNet sense 4 (causing or capable of causing harm):
harmful
From the ODE community, based on WordNet
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