unfounded russian

• несерьёзный

  not serious, unfounded, light, frivolous, unimportant, insignificant

• несостоя́тельность

  insolvency, failure, modest means, unfoundedness, groundlessness, flimsiness, unsoundness

• несостоя́тельный

  insolvent, not wealthy, of modest means, unfounded, groundless, flimsy, unsound, untenable

• необосно́ванный

  groundless, baseless, unfounded, ungrounded

• беспо́чвенный

  groundless, unfounded, unsubstantiated

• голосло́вный

  unsubstantiated, unfounded

• бездоказа́тельный

  unsubstantiated, unfounded

• небезоснова́тельный

  not unfounded

• неоснова́тельный

  groundless, unfounded, lacking foundation, superficial

• несерьёзность

  lack of seriousness, unfoundedness, lightness, frivolity, unimportance

• огу́льный

  groundless, unfounded, indiscriminate, sweeping

Examples

• Э́то совершенно необосно́ванный слух.That's a completely unfounded rumor.