UNIMPEACHABLE
unexceptionable, unimpeachable
(adjective) completely acceptable; not open to exception or reproach; “two unexceptionable witnesses”; “a judge’s ethics should be unexceptionable”
blameless, inculpable, irreproachable, unimpeachable
(adjective) free of guilt; not subject to blame; “has lived a blameless life”; “of irreproachable character”; “an unimpeachable reputation”
unimpeachable
(adjective) beyond doubt or reproach; “an unimpeachable source”
Source: WordNet® 3.1
Etymology
Adjective
unimpeachable (comparative more unimpeachable, superlative most unimpeachable)
Not able to be impeached or reproached.
Blameless.
Beyond doubt.
an unimpeachable alibi
Source: Wiktionary
Un`im*peach"a*ble, a.
Definition: Not impeachable; not to be called in question; exempt from
liability to accusation; free from stain, guilt, or fault;
irreproachable; blameless; as, an unimpeachable reputation;
unimpeachable testimony. Burke.
– Un`im*peach"a*ble*ness, n.
– Un`im*peach"a*bly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition