gradus

/ˈɡɹeɪdəs/

IPA: /G R EY1 D AH0 S/

noun
  1. 1

    A handbook used as an aid in a difficult art or practice, specifically, a dictionary of Greek or Latin prosody used as a guide in writing of poetry in Greek or Latin.

Source: https://en.wiktionary.org/wiki/gradus