According to one theory, related to the PIE adjective *néwos(“new”), allegedly an endingless locative meaning "in the new" (reinforced by the preposition *en(“in”), traces of which can allegedly also be seen in Ancient Greek and Armenian reflexes), from the heteroclitic r/n-stem néwr̥ ~ néwn̥, former of which reflexes can be seen in Ancient Greek νεαρός(nearós, “young, youthful”) and Armenian նոր(nor, “new”). However, prothetic vowels in Greek and Armenian are today usually explained as reflexes of word-initial laryngeal #h₁-, and the evidence is overwhelming that the geminated -νν- of Ancient Greek ἐννέα(ennéa) is of secondary development. The assumption that PIE had a quaternary system (base 4) or octal system (base 8) at some point in prehistory is supported with even less evidence.
Another theory (Blažek 1999:199) takes *h₁néwn̥ to be the accusative of an old primary noun *h₁enu-(“lack”) and thus related to *h₁new(“without”) (whence e.g. Greek ἄνευ(áneu), German ohne).