adj.
Pronunciation: in- ' si-d ē - ə s
Function: adjective
Etymology: Latin insidiosus, from insidiae ambush, from insid ē re to sit in, sit on, from in- + sed ē re to sit ― more at SIT
Date: 1545
1 a : awaiting a chance to entrap : TREACHEROUS b : harmful but enticing : SEDUCTIVE < insidious drugs>
2 a : having a gradual and cumulative effect : SUBTLE <the insidious pressures of modern life> b of a disease : developing so gradually as to be well established before becoming apparent
– in · sid · i · ous · ly adverb
– in · sid · i · ous · ness noun