Possible Clues:

• 18th chapter of a frat
• Letter writer occupied by government flip-flopping
• Greek letter that resembles a rotated M
• Greek letter equivalent to S
• Greek character employed by a general employer retires close to Potchefstroom in South Africa
• Symbol seen in general mathematics appears initially
• The upper case form of this Greek letter indicates addition in mathematics
• Symbol for stock volatility, in finance
• Timeless part of flower as symbol of summer?
• Greek character's mark of disgrace, with time passing