Adjective
Supported by a great deal of evidence.
(linguistics) Of words or languages, proven to exist through a large number of examples or copious records.
Source: en.wiktionary.orgHadrian's military skill is not well-attested due to a lack of military action during his reign; however, his keen interest in, and knowledge of, the army and his demonstrated skill of leadership show possible strategic talent. Source: Internet
The authors note that the relationship is well-attested among other pantherines and primates in the paleontological record. citation The lion's proclivity for man-eating has been systematically examined. Source: Internet