### Clue: Senior officer taking academic stream in philosopher William's place (5)
### Answer: OCCAM 
 ### Explanation: Definition: philosopher William's place
O[fficer] C[ommanding] + CAM (Cambridge river) – reference to William of Occam (or Ockham, which, as I've only just discovered, is a village in Surrey, where he was born), famous for his philosophical "razor"