What kind of synergy does thresh have

Same synergy as with anyone i.o. CC, shield, player movement, and tankiness but when looking the most Fiora builds that aim to be tanks through sustain, that is not having lot of armor/HPs/Mr, I would say the biggest thing Thresh brings to the plate is his automagic tankiness. Thresh rarely has the tower or wave clear but he can stand front of tower for a week with his 200-300 armor while Fiora does the heavy lifting.