well-founded russian

• обосно́ванный

  well-founded, grounded, valid, sound

• малодостове́рный

  not well-founded, unlikely

• малообосно́ванный

  not well grounded, ill-founded

• малооснова́тельный

  not well founded, ill-founded, not reliable

• аргументи́рованный

  well-reasoned, well-founded, argumentative, reasoned, supported by arguments