I've read that some people attribute it to influence from the Slavic languages. But it doesn't just appear in Slavic loans — it also shows up in obviously Latin-derived words like câine 'dog' (from CANEM). On the other hand, not all words with a in Latin have â in Romanian — e.g. FRATER went to frate rather than *frâte. So was this a sporadic sound change, or a regular change conditioned by some environment, or what?
In words of Latin origin, Romanian /ɨ/ arises from a few different places:
- Latin /a/ followed by /n/: cânt < canto, sfânt < sanctum. The diphthong in pâine, câine is due to assimilation to the following vowel.
- The Latin word /in/. This is not a regular sound change in that not all Latin instances of /i/ followed by /n/ are centralized, but all forms of the preposition "in" have /ɨ/.
- The vowel /i/ preceded by /rr/ or initial /r/: râu < rivum, urî < horrire.
Other instances of /ɨ/ are generally loans. Also, there are numerous words of Latin origin which appear to violate the rules above, but these are usually later reborrowings from Latin or sometimes French.