Insidious russian

• кова́рный

  insidious cunning or crafty

• кова́рство

  insidiousness

  deceit or cunning

  Inclination to insidious intentions and actions

• ехи́дный

  malicious, spiteful, venomous, insidious, sarcastically

• астра́л

  astral

  Insidious (horror film series)

• злоко́зненный

  insidious, crafty, wily

• вкра́вшийся

  sneaked in, crept in, insidious, hidden

• подка́пывающийся

  undermining, sapping, subversive, insidious

• ехи́дство

  malice, spite, insidiousness

• коварно

  insidiously, treacherously, perfidiously, craftily, maliciously

Examples

• Э́то очень кова́рная боле́знь. Ты не заме́тишь её, пока не будет слишком поздно.

  That's a very insidious disease. You don't notice it until it's too late.