Could it be a variant spelling of Ceci - many possible versions - a nickname for Cecily or Cecilia? Or is it what you thought it would be spelt like, based on what you heard?
I don't know if it is a nm of Cecily or Cecilia. I found the spelling by doing searches of JonathanAnton and that is how she spells it. We do like the Sescie spelling and it's what we are going with it. Thanks for the lead!