By way of being six to one (3)
I believe the answer is:
via
'by way of' is the definition.
(I've seen this in another clue)
'six to one' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'to one' becomes 'a' (a thing is one thing).
'vi'+'a'='VIA'
'being' acts as a link.
(Other definitions for via that I've seen before include "By means of" , "By way of - in Latin" , "Roman road" , "A Roman way" , "Passing through" .)