Capable of being attested to, confirmed, or proven through evidence or testimony.
From 'attest' (from Latin 'attestari': 'ad-' + 'testis' meaning witness) combined with the suffix '-able' indicating capability or possibility.
In law and historical research, facts are only valuable if they're 'attestable'—meaning you can actually prove them through witnesses or documents, which is why court testimony is so formal.
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