insidious
1. [ adjective ] intended to entrap
Related terms: dangerous
2. [ adjective ] beguiling but harmful
Examples:

"insidious pleasures"

Related terms: seductive
3. [ adjective ] working or spreading in a hidden and usually injurious way
Synonyms: subtle pernicious
Examples:

"glaucoma is an insidious disease" "a subtle poison"

Related terms: harmful
Similar spelling:   insidiously
  injudicious
  iniquitous
  incautious
  in_stride
  inside
  inside-out
  inside_out
  insider
  iniquitously
  incautiously