What is "hereswith"

Hereswith or Hereswitha , also spelt Hereswithe, Hereswyde or Haeresvid, was a 7th-century Northumbrian saint. She married into the East Anglian royal dynasty and afterwards retired to Gaul to lead a religious life. Hereswith's sister was Saint Hilda (or Hild), founder of the monastery at Whitby. Details of her life and identity come from Bede's Historia Ecclesiastica, the Anglian collection and the Lives of Edwin of Northumbria and Hilda of Whitby.