noun
1. archaic : a parish church
the mother churches … and rural chapels in the late Saxon and early Norman periods — Bulletin of Institute of Historical Research
2. : the principal church of a locality or land ; specifically : a cathedral or a metropolitan church
the mother church … which no visitor to these parts should fail to see — T.I.Ellis
3. : the original church from which others have sprung
the mother church of Unitarianism in America — Leo Pfeffer
4. : the original church or communion in which a person has been nurtured
returning to his mother church, he died in obscurity — K.S.Latourette