Possible Clues:

• Is it cold under sunhat, one discussed
• Theme of Plato, picked up by Aristotle
• We may discuss this item of headgear, having got cold
• Subject -- best one college offers
• Subject to choose for hearing
• Issue (for discussion)
• Subject gets to choose when king is finally expelled
• 'Theme, subject (5)'
• Debate choice
• Subject (of speech, etc)