unsubstantiated

adjective

un·​sub·​stan·​ti·​at·​ed ˌən-səb-ˈstan(t)-shē-ˌā-təd 

: not proven to be true : not substantiated

an unsubstantiated rumor/report

a plausible but unsubstantiated theory

Synonyms

• baseless
• foundationless
• groundless
• invalid
• nonvalid
• unfounded
• unreasonable
• unsupported
• unwarranted

Examples of unsubstantiated in a Sentence

an unsubstantiated claim that was thrown out of court

Recent Examples on the Web

That was followed by a public spat between the two men, Musk making the unsubstantiated claim that Trump is named in the Epstein files and calling for the impeachment of the president. —Martha McHardy, MSNBC Newsweek, 13 June 2025

The unsubstantiated claims took hold after the president, who will turn 79 on Saturday, stumbled while boarding Air Force One last weekend. —Peter Suciu, Forbes.com, 12 June 2025

ByteDance has denied these claims, which remain unsubstantiated. —Greta Cross, USA Today, 6 June 2025

Trump fired Krebs, who directed the Cybersecurity and Infrastructure Security Agency, in November 2020 after Krebs disputed the Republican president’s unsubstantiated claims of voting fraud and vouched for the integrity of the 2020 election, which Trump lost to Democrat Joe Biden. —Rebecca Santana, Los Angeles Times, 3 June 2025

Word History

First Known Use

circa 1775, in the meaning defined above

Rhymes for unsubstantiated

• ameliorated
• decontaminated
• deoxygenated
• deteriorated
• differentiated
• disarticulated
• excommunicated
• incapacitated
• individuated
• misappropriated
• monounsaturated
• multinucleated