Longman Dictionary of Contemporary English
unchallengeable
adjective
EXAMPLES FROM CORPUS
▪ And even if, I repeat their findings were valid, enough unchallengeable evidence would remain to make them immaterial.
▪ As his mouth opened, Alan saw the gaps in his teeth, but his voice and his movements seemed unchallengeable.
▪ By contrast, the appeal of the industrial co-operative remains unchallengeable, its ecological niche exclusive to it.
▪ Certain principles and values are assumed to be unchallengeable and therefore to be nurtured.
▪ Indeed little of what had been unchallengeable orthodoxy since the 1920s remained untouched.
▪ Many leading scientists do not consider that science can give absolutely reliable and unchallengeable knowledge.
▪ The assertion that some particular type of conduct is morally wrong because it is may appear unsatisfactory but it is unchallengeable.
▪ When the procedure is correctly observed it is virtually unchallengeable.
Wiktionary
unchallengeable
a. Not open to challenge; indisputable
WordNet
unchallengeable
adj. not open to challenge; "unchallengeable facts"; "a position of unchallengeable supremacy"
Usage examples of "unchallengeable".
Yet to Margaret there was something identifiably American about these missing boys, a kind of cocksure combination of mischief and unstoppable optimism—as if each of them thought that his opinion would always be unchallengeable, his car never in the wrong lane.
Morphy soft-voiced and utterly dull pointed out one unchallengeable truth after another.
In England its position was strong but not unchallengeable, and outside England all the points were in the hands of its enemies.