### Clue: Route travelled by sea was up for discussion (4)
### Answer: ROAD 
 ### Explanation: Definition: Route travelled by sea
  **Homophone of**(for discussion) "rode",was up on a horse
Answer:  I'm not sure of the explanation here.  "Roads" (in the plural) are partly sheltered areas near shore, where ships can anchor, whereas "road" is a route travelled, but not necessarily by the sea.  Any ideas anyone?