thistle-dollar

from The Century Dictionary.

• noun A silver coin of Charles II. of England, struck in 1676: so called from emblems on the reverse.
• noun A Scottish silver coin, also called the double merk, issued in 1578 by James VI. It weighed 342.6 grains troy, and was worth 23s. 8d. Scotch (nearly 2s. English) at the time of issue.