E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Money. Shakespeare, in The Merry Wives of Windsor, ii. 2, has Money is a good soldier, sir, and will on. Doubtless the French use of
the word is derived from the proverbial truth that Money is the sinews of war, combined with a pun on the word solidus (the pay of a soldier). The Norman soud (i.e. sould) means wages; Swedish, besolda, to pay; Danish, besolde, to pay wages; the French soldat, our soldier, a hireling or mercenary, and the French sol or sou.