Oscan assumes a pre-eminent position among the group, because of the political power and geographical extent of its' speakers. The Oscan orthography is descended from the Etruscan model, and thus lacks a letter O; in approximately 300 B.C., two letters - and s - were added to the alphabet, the latter of which was used for the sound /o/. For the voiced consonants /g/ and /d/, the symbols C and R were used, respectively.
As far as the grammar is concerned, Oscan was the most archaic and conservative among Italic languages. It preserved practically all Indo-European diphthongs, most of noun endings were quite close to Indo-European ones. Oscan is believed to be the only Italic tongue who did not know rotacism (s > r between vowels), and the Common Italic structure of declension was kept there with its significant endings -asm (gen. pl. of -stems) and -d (ablative sg. of o-stems). Oscan had a famous Osco-Umbrian p instead of Indo-European kw (which took Oscan closer to Celtic tongues). The verb had a structure similar to that in Latin and other Italic languages: infect and perfect times, passive endings in -r, future imperative. The infinitive in Oscan ended in -um.
Oscan language was assimilated by Latin since
the 4th century BC, when Rome began to conquer Samnitian lands. But still,
much is known about the language because of some texts found in Italy (Cippus
Abellanus and others). But in fact, there is much unknown as well.