Possible Clues:

• Omicrons' predecessors
• Greek letters after nus
• Some fraternity row letters
• Greek letters near the end of the English dictionary
• Followers of the nus?
• ''__ for xylophone''
• Ones following the nus?
• Letters from abroad a number sent up
• Expected 2015 Sue Grafton title starter
• Letters from abroad: at least twenty two?