Related Clues:

• Certain Greek letter
• The Greek 's'
• Greek letter `S'
• The 18th letter of the Greek alphabet
• The American serviceman's got back to his mother with a letter from Greece
• "The Sweetheart of ___ Chi"
• Agism of the Greek letter
• Letter on a house used by 4-Across
• Head of ancient Sparta?
• S, as in Socrates
• Greek 'S'
• Summation symbol in math
• Brand without the T that comes before it
• Freud dismissed German and added to 'A Letter to Plato'
• One of those letters from abroad soldiers sent back to mum