mother lode

Or moth·er·lode

[muhth-er-lohd]

noun

1. Mining.,  a rich or important lode.

2. a major or profitable source or supply.

   New York City is a mother lode of actors.

mother lode

noun

1. mining the principal lode in a system

Word History and Origins

Origin of mother lode¹

First recorded in 1855–60