Wherefore art thou, aberil?

[Mauro]

Anyway. Having the 'b' in April is already not common, so for me it is worth it to continue the search.

I agree of course. Maybe an expert in the phonetics (and history of phonetics) of European languages could give some informed opinion about which language could have been more likely, phonetically, to have or develop the form 'aberil' around the 1400s? But it looks to be a hard question too.