9 letters · 10 points in Scrabble
adjective beguiling but harmful
adjective intended to entrap
adjective working or spreading in a hidden and usually injurious way
originFrom 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”).
Etymology from Wiktionary, CC BY-SA 3.0