(Des). 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.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894