"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."
<a href="https://www.etymonline.com/word/diagnoses">Etymology of diagnoses by etymonline</a>
Harper, D. (n.d.). Etymology of diagnoses. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/diagnoses