Sovereign support for a firm line (5)
I believe the answer is:
ruler
'sovereign' is the definition.
(I've seen this in another clue)
'support for a firm line' is the wordplay.
I cannot really understand how this works, but
'line' could be 'rule' (I've seen this in another clue) and 'rule' is found within the answer.
A single letter 'r' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ruler that I've seen before include "leader in government" , "Man in charge" , "Strip with straight edge to measure" , "liner?" , "Measuring tool" .)