insidiously
1. [ adverb ] in a harmfully insidious manner
Synonyms: perniciously
Examples:

"these drugs act insidiously"

Related terms: insidious baneful baneful insidious
Similar spelling:   insidious
  insidiousness
  injudiciously
  injudicious
  iniquitously
  incautiously
  iniquitous
  incautious
  in_stride