The term 'curved letter' can refer to three different crossword solutions: ESS (3 letters), CEE (3 letters), and ESSES (5 letters). ESS is an abbreviation for the letter S, which is a common curved letter in the English alphabet. CEE is an abbreviation for the letter C, which is also a curved letter in the English alphabet. Finally, ESSES is an abbreviation for the letter SS, which is two S's side by side, making it a double curved letter.