-urnus

• -rnus

Ultimately from the adjective-forming suffix -(i)nus; see also -rnus. Szemerényi 1959 proposes that the starting point was pre-Latin *hesterinos (hesternus) and *wesperinos (reconstructed based on the obsolete word vesperna). As a result of rebracketing, the *-erinos at the end of these words would have been attached to *diw- and *nokt-, the pre-Latin roots of the words diēs (“day”) and nox (“night”), initially forming *diw-erinos and *nokt-erinos. Szemerényi argues that *diw-erinos was syncopated to *diwrinos and then regularly developed to *diurnos (Latin diurnus), and then the ending *-urnos was extended by analogy to nocturnus and other words. Others have argued that the adjectives may have been formed on or influenced by the adverbs diū/diūs (“by day”) and noctū (“at night”).

• (Classical Latin) IPA^(key): [ʊr.nʊs]
• (modern Italianate Ecclesiastical) IPA^(key): [ur.nus]

-urnus (feminine -urna, neuter -urnum); first/second-declension suffix

1. Enlargement of -nus (suffix forming adjectives).

   ‎albus + ‎-urnus → ‎alburnus

   ‎diū (comparative stem: diūt-) + ‎-urnus → ‎diūturnus

   ‎nox (oblique stem: noct-) + ‎-urnus → ‎nocturnus

   ‎tacitus + ‎-urnus → ‎taciturnus

First/second-declension adjective.

• “-urnus” on page 2,107/2 of the Oxford Latin Dictionary (1st ed., 1968–82)
• Szemerényi, Oswald (1959) “Latin hībernus and Greek χειμερινός”, in Glotta, volume 38, number 1./2. H., pages 107-125