1. 无可怀疑的；完全可靠的
If you describe someone as unimpeachable, you mean that they are completely honest and reliable.

1. completely acceptable
not open to exception or reproach

e.g. two unexceptionable witnesses
a judge's ethics should be unexceptionable

Synonym: unexceptionable

2. free of guilt
not subject to blame

e.g. has lived a blameless life
of irreproachable character
an unimpeachable reputation

Synonym: blamelessinculpableirreproachable

3. beyond doubt or reproach

e.g. an unimpeachable source