Synonyms of unsubstantiated

unsubstantiated

adjective

ˌən-səb-ˈstan(t)-shē-ˌā-təd 

as in unreasonable

having no basis in reason or fact

an unsubstantiated claim that was thrown out of court

Synonyms & Similar Words

• unreasonable
• unfounded
• baseless
• unsupported
• unwarranted
• groundless
• false
• irrational
• invalid
• unreasoned
• unnecessary
• misleading
• absurd
• illogical
• fallacious
• foundationless
• implausible
• inconsistent
• nonvalid
• specious
• weak
• unconvincing
• unconscionable
• meaningless
• untenable
• misled
• gratuitous
• wrong
• unsound
• flimsy
• stupid
• uncalled-for
• nonsensical
• fatuous
• foolish
• nonlogical
• preposterous
• asinine
• silly
• insane
• ill-advised
• unwise
• wacky
• simpleminded
• harebrained
• nutty
• crackpot
• mad
• senseless
• brainless
• crazy
• half-witted

Antonyms & Near Antonyms

• reasonable
• valid
• good
• justified
• hard
• reasoned
• confirmed
• just
• substantiated
• certified
• well-founded
• logical
• rational
• informed
• well-grounded
• actual
• true
• real
• validated
• sensible
• wise
• certain
• genuine
• verified
• corroborated
• sane
• sober
• sure
• clear
• plausible
• solid
• credible
• compelling
• convincing
• sound
• persuasive
• commonsense
• satisfying
• cogent

Example Sentences

Recent Examples of unsubstantiated

Those efforts were aided by Canary Mission and Betar, two pro-Israel groups that maintain online lists of Israel’s critics, often alongside unsubstantiated claims that they are affiliated with Hamas, according to the lawsuit. — Jake Offenhartz, Fortune, 15 July 2026

Conjecture over that evidence has fueled unsubstantiated conspiracy theories that there might have been a second shooter or that Kirk’s death was staged. — Hannah Schoenbaum, Chicago Tribune, 11 July 2026

Yoon, who faces other criminal cases as well, has promoted unsubstantiated election fraud claims circulated on YouTube to defend his botched power grab and rally conservative supporters against the Democrats. — ABC News, 7 July 2026

In spite of the rhetoric and unsubstantiated claims, highways don’t equal economic development. — Pete Harrison, Hartford Courant, 6 July 2026