1. in a way that cannot be questioned, criticized, or doubted; beyond reproach

Examples

• Her research methods were unimpeachably thorough and scientific.
• The judge’s reputation was unimpeachably honest throughout his career.
• The witness testified unimpeachably about what she had seen.
• His credentials were unimpeachably impressive to the hiring committee.
• The evidence was presented unimpeachably by the prosecution.
• She conducted herself unimpeachably during the investigation.