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 of unsubstantiated

• unreasonable
• unfounded
• baseless
• unsupported

Examples of unsubstantiated in a Sentence

an unsubstantiated claim that was thrown out of court

Recent Examples on the Web

Conjecture over the evidence in Kirk’s killing has fueled unsubstantiated conspiracy theories that there might have been a second shooter, or that his death was staged. — Rebecca Boone, Chicago Tribune, 22 June 2026

On Facebook, TikTok and Instagram, unsubstantiated claims often go unchecked. — Duaa Eldeib, ProPublica, 12 June 2026

The resolution’s author, Assemblymember Marc Berman, D-Menlo Park, also connected it to a string of unsubstantiated accusations Trump has made in the last week about California ballot counting. — Stephen Hobbs, Sacbee.com, 10 June 2026

For the past several months, Owens has waged a digital terror campaign against Erika Kirk, spreading conspiracy theories about her husband’s death (and appearing to imply that Erika was involved in covering it up, an unsubstantiated narrative that somehow also involves Israel and Tucker Carlson). — Elaine Godfrey, The Atlantic, 9 June 2026

Word History

First Known Use

circa 1775, in the meaning defined above

Rhymes for unsubstantiated

• abbreviated
• accelerated
• accentuated
• accommodated
• acculturated
• accumulated
• acidulated
• adjudicated
• administrated
• adulterated
• affiliated
• agglomerated