insidious

Meanings

1. 1
   adj

   working or spreading in a hidden and usually injurious way

   Glaucoma is an insidious disease.

2. 2
   adj

   beguiling but harmful

   Insidious pleasures.

From Middle French insidieux, from Latin īnsidiōsus (“cunning, artful, deceitful”), from īnsidiae (“a lying in wait, an ambush, artifice, stratagem”) + -ōsus, from īnsideō (“to sit in or on”), from in (“in, on”) + sedeō (“to sit”).

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