Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† pĕtăsĭo and pĕtăso, ōnis, m., = πετασών, a leg or pestle of pork, esp. the shoulder (opp. perna, the ham): e Galliā apportantur Romam pernae tomacinae et taniacae, et petasiones, Varr. R. R. 2, 4, 10: pulpam dubio de petasone voras, i. e. that has already begun to turn, Mart. 3, 77, 6.