‘Eglwys’ means church and ‘Gwyddelod’ is the word for ‘the Irish’, so this site’s name probably means ‘The Church of the Irish’.
However, there’s another less common meaning for the word ‘Gwyddelod’ (probably developed on the basis of misinterpretation of the word ‘gwydd’) which is an old word for ‘woods/trees’ etc. This means the circle’s name might mean ‘The Church of the Trees’.
Big thanks to Elin for her help translating this, and providing most of the other Welsh language info that I’ve posted.
Kammer x