Would "manman" in "manman lajan" mean "huge pile of money" and in what other ways can you use "manman"?

Manman lajan is a sum of money on which interest may be paid. It's the principal amount (of money).

Haitians us manman as an interjection (and papa too):
Adye manman!
Adye papa!

And they also use it to say big, huge, massive
(They use papa the same way too.)
yon gwo manman kay
yon manman bèf
yon manman kanson
etc...

Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words