Govern by regulation? (4)
I believe the answer is:
rule
I believe this is a double definition.
'govern' is the first definition.
(I know that govern can be written as rule)
'regulation?' is the second definition.
(I know that regulation can be written as rule)
'by' is the link.
(Other definitions for rule that I've seen before include "Control using lure." , "Dominate" , "Standard" , "Determination" , "Reign - law" .)