It is first and foremost the name of a saint. I don't know what it means. I'd guess it derives from 'portere' meaning 'to carry'. This could be consistent with this saint being a slave (i.e. porter?) before becoming a monk.
'A one time slave, he became a monk after gaining his freedom and eventually became the abbot of a monastery in Auvergne, Gaul. He is known to have compelled the Frankish Merovingian king
Thierry I of Austrasia into releasing various prisoners from the dungeons.'