One day, Frederick invited Voltaire to come join him at his castle, Sanssouci, in Potsdam, by writing the following note:
_p__ à _ci__
Voltaire did not miss a beat and replied with his own note:
And they both began to look forward to their next meeting!
Voltaire immediately understood Frederick’s note to mean “venez souper à Sanssouci“–ie, come dine at Sanssouci. The word venez is “sous” (under) the letter p. The word sans is “sous” the word ci.
So he replied by saying J’ai grand appétit: Capital G = “Gé grand”; lower-case a = “a petit”.