The lexeme remains unexplained, and there does not seem to be any etymological basis in considering it a synonym or equivalent term for the variant reading blanc poi (‘white pitch’). The DMF has an entry pestot but its sense (‘Pilon ; masse ou massue’) does not seem to be relevant here. Finally, the word may perhaps be read as pestocce, in which case it could be interpreted, formally at least, as a variant spelling of pistace.