Guinea

British monetary unit equal to £1.05, i.e., 21 shillings. In case you are not already in on the secret, there is no longer any such coin or paper money. For further details see Patience.

There was an old man from Kilkenny,
Who never spent more than a penny
  At any one loo,
  But this could accrue
On long walks to more than a guinea.

Pronunciation: 
ginny
Context: 
and paid a guinea to a toilet club
Opera: 
Act: 
Act II