Diagnosis

google

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late 17th century: modern Latin, from Greek, from diagignōskein ‘distinguish, discern’, from dia ‘apart’ + gignōskein ‘recognize, know’.

wiktionary

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From Latin diagnōsis, from Ancient Greek διάγνωσις(diágnōsis), from διαγιγνώσκω(diagignṓskō, “to discern”), from διά(diá, “through”) + γιγνώσκω(gignṓskō, “to know”).

etymonline

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diagnosis (n.)

"scientific discrimination," especially in pathology, "the recognition of a disease from its symptoms," 1680s, medical Latin application of Greek diagnōsis "a discerning, distinguishing," from stem of diagignōskein "discern, distinguish," literally "to know thoroughly" or "know apart (from another)," from dia "between" (see dia-) + gignōskein "to learn, to come to know," from PIE root *gno- "to know."