Derivation of a phrase

Factual Questions
1

I am SO in need of this one - my only suggestions so far are NOT very persuasive. Besides - why only protect one?

The phrase is “covering the nut” or “cover your nut”. The general meaning is that the business has made enough profit to cover the expenses and now any additional profit is going to be the net profit for the month.

Can you help?

Gracias

2

Definition #10 for “nut” in Merriam-Webster’s Collegiate Dictionary at Brittanica.com: “the amount of money that must be earned in order to break even.”

3

The Word Detective’s etymology:

http://www.word-detective.com/071000.html#nut