John Marincola has defined Polybius as ‘a highly intrusive explicator’ of his own narrative.1 Polybius regularly interrupts the main narrative of events to explain and clarify what procedure he is following. Such intrusions always retain a historiographical flavour, and Polybius comes up with words or expressions used in a new way and with a new nuance, which I define as ‘historiographical neologisms’. This chapter will show how Polybius inserts himself into a tradition (which he criticizes as well) in order to establish his own authority, and will highlight two ways: borrowing and revisiting terms from other genres – the much-discussed apodeiktike historie is a famous example2 – to give them a historiographical nuance, or creating new ones.