What is a guinea coin?

  The guinea is an English gold coin. Its name arises from the fact that it was coined first from gold obtained in Guinea. It is equivalent to twenty-one shillings, and corresponds closely to our five dollar gold piece. It was first coined in 1663, in the reign of Charles II, whose profile appeared on one face of it. Directly beneath the head of the king is a miniature figure of an elephant. The coinage was discontinued in 1817, but the guinea is still used in accounts. The term is rather poetic. Burns says:

   The rank ís but the guinea's stamp 
   A man's a man for a' that.

Tennyson also uses the term:

   But the jingling of the guinea helps the hurt that Honour  feels.