Fromgold +‎back.

goldback (pluralgoldbacks)

1. A unit of the Goldbackcurrency system containing 1/1000th of atroy ounce of puregold
2. (countable,US,slang,historical) A kind ofgold certificate with an orange back.

   Synonym:yellow boy

3. Any member of speciesPentagramma triangularis of ferns.
4. Any member of genusPityrogramma of ferns.

• black dog