underhandedly
1. [ adverb ] slyly and secretly
Synonyms: underhand
Examples:

"Mean revenge, committed underhand"- John Donne "oldline aristocratic diplomats underhandedly undermined the attempt...to align Germany with the Western democracies"- C.G.Bowers

Similar spelling:   underhanded
  understandably
  understandingly
  understand
  undermanned
  undersurface
  understaffed
  understanding
  understate
  underspend
  underframe
  understandable
  undergraduate
  underworld
  understated
  undersealed
  undercoated
  undercharge
  under_wraps