*rūmōniz

Back-formed from the plural *Rūmōnīz, from Latin Rōmānī, itself the plural of Rōmānus.

At the time of borrowing, *ō was still pronounced as a more open vowel ā, probably /ɒː/. Since Proto-Germanic did not possess a long *ō at that time, the closest vowel to the Latin ō was Proto-Germanic *ū. Therefore, the word was probably borrowed from Latin as *Rūmānīz. At that time, Proto-Germanic had not yet completed the full shift from ā to ō, since the shift affected this loanword as well when it did occur, changing *Rūmānīz to *Rūmōnīz. This provides evidence that the shift occurred around or shortly after the first contact between Romans and Germanic tribes, which cannot have been later than the Battle of Noreia in 112 BCE.