Green’s Dictionary of Slang

big mama n.2

[euph. for SE big + motherfucker n. (2)]

1. anything notably large, substantial; also as adj.

[US]L. Dills CB Slanguage 11: Big mama: 9-foot whip antenna.
www.audioasylum.com 🌐 What about a parafeed type output? No DC through the transformer, no need for it to be a big beefy mutha [...] Hmmm... if you mean one with a resistor – that one is inefficient, and the one with a coil – now that’s one big mama coil.

2. (US) the ocean.

[US]D. Burke Street Talk 2 56: The big mama’s fully macking insanely gnarly grinders.