motherhouse

Short definition from Wiktionary

Noun

1. 1
   The monastery from which the other 'houses' of a religious order or congregation were (directly or indirectly) founded, often eponymous.
2. 2
   The convent which is the seat (and often the above original foundation) of the superior of an order or congregation, and/or on which lower ranking houses (such as priories under an abbot) depend.