Marked thus $, either scutum or 8, a dollar being a “piece of eight” [reals]. The two lines indicate a contraction, as in lb.
The word is a variant of thaler (Low German, dahler; Danish, daler, and means “a valley,” our dale. The counts of Schlick, at the close of the fifteenth century, extracted from the mines at Joachim's thal (Joachim's valley) silver which they coined into ounce-pieces. These pieces, called Joachim's-thalers, gained such high repute that they became a standard coin. Other coins being made like them were called thalers only. The American dollar equals 100 cents, in English money a little more than four shillings.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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