Origin: Latin suffix -able
Unimpeachable has 4 different meanings across 1 category:
free of guilt; not subject to blame
"has lived a blameless life"
"of irreproachable character"
"an unimpeachable reputation"
completely acceptable; not open to exception or reproach
"two unexceptionable witnesses"
"a judge's ethics should be unexceptionable"
Not able to be impeached or reproached.