un ‧ chal ‧ lenge ‧ a ‧ ble /ʌnˈtʃæləndʒəb ə l, ʌnˈtʃælɪndʒəb ə l/ BrE AmE adjective
[ Word Family: adjective : ↑ challenging , ↑ challenged ≠ ↑ unchallenged , ↑ unchallengeable ; noun : ↑ challenge , ↑ challenger ; verb : ↑ challenge ; adverb : ↑ challengingly ]
1 . a belief, idea etc that is unchallengeable is definitely true and cannot be questioned or argued with:
unchallengeable evidence
2 . if someone’s power or authority is unchallengeable, it cannot be taken from them