mother church

Short definition from Wiktionary

Noun

1. 1
   The Church regarded as nourishing and protecting its members.
2. 2
   A church with oversight over another or others, now especially a cathedral or metropolitan church.
3. 3
   The original church of a denomination, regarded as having birthed the others.
4. 4
   The original denomination or community of believers from which other denominations and communities of believers sprang.