Governs by regulations? (5)
I believe the answer is:
rules
I believe this clue is a double definition.
'governs' is the first definition.
(I know this)
'regulations?' is the second definition.
(I know this)
'by' is the link.
(Other definitions for rules that I've seen before include "is supreme, OK?" , "Governs; regulations" , "Reigns" , "Is king" , "Laws; draws lines" .)