Roasio

This surname originates from the Piedmont region of Italy. It is most likely derived from Roasio, which is the name of a municipality in that same region. The meaning of the municipality's name is uncertain, but since it is located in Piedmont and known as Roaso in the Piedmontese language, the etymological origin of the name is most likely Piedmontese. Roasio would then be the italianized form of the actual Piedmontese name (instead of vice versa). The municipality was known as Rovaxida(m) or Rovaxidum in early medieval times, which might suggest that Roasio (or Roaso) is actually a shortened form of the original name. One source claims that the name is related to the Piedmontese word ruai meaning "thorny bush, thicket" as well as "bramble", which itself is probably etymologically related to Italian roveto "thorny bush, bramble" and Latin rubus "bramble, blackberry bush".

With that said, it should be noted that there is also a source that claims that the surname of Roasio is derived from the late medieval Italian given name Rubasio (or Rovasio), which is said to come from the Late Latin given name Rubasius. I can find no evidence that this was an actual given name in medieval Italy, however, so this etymological explanation doesn't appear very plausible (at least when compared to the etymological explanation that was provided earlier).

Lastly, you might want to take a look at the surname Roascio, which is also of Piedmontese origin and might possibly be etymologically related.