insidious
/ɪnˈsɪdi.əs/ adjective
- adjective Causing harm in a stealthy, often gradual, manner.
- adjective Intending to entrap; alluring but harmful. “Hansel and Gretel were lured by the witch’s insidious gingerbread house.”
- adjective (nonstandard) Treacherous. “The battle was lost due to the actions of insidious defectors.”
Synonyms
subtle perfidious proditorious traitorous booky dastardly disleal disloyal double-crossing double-dealing double-faced double-hearted doublehearted faithless false falseheart false-hearted guiled guileful hollow-hearted pernicious
Etymology
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”).
Webster’s 1913
- adjective Lying in wait; watching an opportunity to insnare or entrap; deceitful; sly; treacherous; --said of persons; as, the insidious foe. "The insidious witch." Cowper.
- adjective Intended to entrap; characterized by treachery and deceit; as, insidious arts.
Etymology [L. insidiosus, fr. insidiae an ambush, fr. insidere to sit in; pref. in- + sedere to sit: cf. F. insidieux. See Sit.]
Sources: Wiktionary · WordNet 3.0 · Webster’s 1913 — from the Wiktionary entry “insidious”, CC BY-SA 4.0. Details