What is the origin of the word dough as in “money”?
Well, let’s talk about dough “uncooked bread”, first. It has an interesting history. It goes back to Old English dag “dough”, which derives from the Indo-European root *dheigh – “to form, to knead”. That root gave us the prehistoric Germanic *daigaz “something kneaded”, which gave rise to German teig, Dutch and Swedish deg, Danish dej, all meaning “dough”. The Indo-European root gave related words to other languages, such as Gothic digan and Avestan diz “mold, form”. Avestan was a dialect of Old Iranian, and it is from diz that we get the last element in the word paradise (literally “a walled garden” and, etymologically, the “place around which a wall is shaped”).
Another English word related to dough is, perhaps surprisingly, lady. It derives ultimately from Old English hlaefdige “kneader of bread”, the – dige coming from *dheigh-. The hlaef element is related to modern English loaf [of bread].
Now, why is dough a slang term for “money”? For the same reason that bread is: one needs bread (food) to live, and money is what buys it. Dough is simply another word for bread, or vice versa. That usage of dough dates from the 19th century in the U. S. and spread to Britain and elsewhere thereafter. One source reports that there is even Cockney rhyming slang for that use of dough and that is cod’s (short for cod’s roe).