An English slang term for a Guinea or Sovereign, the reference being, of course, to its color.
Arbuthnot, in The History of John Bull , 1713, uses the expression " there wanted not yellow-boys to fee counsel. "
That the name at a later period was also common in Scotland and Ireland, the fol- lowing quotations indicate : Alexander Boswell, in his Poetical Works , edition 1871 (p. 205), has the lines: " Though up in life, I'll get a wife, I've yellow boys in plenty." and T. C. Croker, in Fairy Legends and Traditions of South Ireland, 1862 (p. 308), says: " Fill your pockets with these yellow boys."
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)