insidious insidious /ˌɪnˈsɪˌdiːəs/

adjective

1. Working or spreading in a hidden and usually injurious way  ( insidious , pernicious , subtle )
   working or spreading in a hidden and usually injurious way
    Glaucoma is an insidious disease
   glaucoma is an insidious disease
    A subtle poison
   a subtle poison
   
2. Intended to entrap  ( insidious )
   intended to entrap
   
3. Beguiling but harmful  ( insidious )
   beguiling but harmful
    Insidious pleasures
   insidious pleasures