An Etymological Dictionary of Astronomy and Astrophysics

1. The process of determining by examination the nature and circumstances of a diseased condition.
   

   2. The decision reached from such an examination.
      

   3. Scientific determination; a description that classifies a group or taxon precisely; a determining or analysis of the cause or nature of a problem or situation (Dictionary.com).

Etymology (EN): L., from Gk. diagnosis “a discerning, distinguishing,” from stem of diagignoskein “discern, distinguish,” literally “to know thoroughly,” from dia- “through” + gignoskein “to learn,” cognate with Pers. šenâs-, šenâxtan “to know, to be acquinted” and dânestan “to know,” as below, ultimately from PIE root *gno- “to know.”

Etymology (PE): Parnâs, from par- “through,” + nâs “to know,” as in Zazaki nâs- “to know,” Kurd. nâs-, nâsîn “to know,” related to Pers. šenâs- “to know,” related to šenâxtan, → knowledge and
dânestan, → science.