At this moment, DEX (Dicționarul Explicativ al Limbii Române, the standard dictionary of the Romanian language) has no entry that will prove the existence of the word or try an explanation. However, the word koson is frequently used in scientific articles and books. Koson is preferred by scholars who follow the name as it is spelled on the coins, while others use coson, in connection with the Latin spelling of the name Cotiso (Coson) in ancient sources.
”Because most of the scholars – we quote amongst others Max von Bahrfeldt, Iudita Winkler and Octavian Iliescu – believe that is a real king, Cotiso or even Coson, mentioned by Romans (Horatius, Suetonius, Florus), we consider it proper to use the Latin way of spelling the name: king Coson and cosons for his coins.”
Carmen Maria Petolescu, Monedele regelui Coson p. 11, Note 6