unimpeachable.

So reliable, sound, or honorable that it cannot reasonably be called into question.

Use it for

Words that belong together

• unimpeachable evidence
• unimpeachable integrity

On the page

The evidence appeared unimpeachable until its chain of custody was examined.

Her unimpeachable integrity made the accusation harder to sustain, not impossible to investigate.

Usage notes

Primary category: literary. Forms: Normally non-gradable adjective. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.