### Clue: Cab heading off to the centre of Rome? It's taken for granted (5)
### Answer: AXIOM 
 ### Explanation: Definition: It's taken for granted
  tAXI(*cab*, taxi without its initial letter,*heading off*) +(*to*) OM(letters in *centre of *the word *Rome*).
Defn:  A statement that is *taken* to be self-evident,*for granted*, and thus forms the basis for further arguments and conclusions.