The Roman way of deviation (3)
I believe the answer is:
via
'the roman way' is the definition.
(term for a street in Italian eg in Rome)
'of deviation' is the wordplay.
'of' says the answer is hidden in the clue.
'VIA' can be found hidden inside 'deviation'.
(Other definitions for via that I've seen before include "A Roman way" , "Passing through" , "By means of" , "Roman road" , "By way of - in Latin" .)