Green’s Dictionary of Slang

(US) $1; money in general.

[1877		E.L. Wheeler Deadwood Dick in Beadle’s Half Dime Library I:1 87: But, now that we are counting eggs, how much of the ‘lay’ is to be mine].
1900		Nat. Police Gaz. (NY) 22 Sept. 11/3: Several of the ‘boys’ looked forward to the inevitable termination of a profitable industry and wisely, ‘hid an egg’.
1900		Nat. Police Gaz. (NY) 10 Nov. 7/1: That he is in line for the ‘eggs’ is evident.
1912		Ade Knocking the Neighbors 71: Papa...began to sign Checks. It took many an egg to have Lila properly Conservatoried.