Possible Clues:

• Math expression with two terms
• Provides two names for caddy with nothing to mail surprisingly
• School's latest intention: old writer to turn up, covering two terms
• Like an "a + b" expression
• (Of an equation) consisting of two terms - in a limbo (anag)
• By the sound of it, don't buy any meal in such a two-term mathematical way
• Algebraic expression of two terms linked by + or -