Monarch ready to draw the line (5)
I believe the answer is:
ruler
'monarch' is the definition.
(I've seen this before)
'draw the line' is the wordplay.
'draw' becomes 'rule' (ruling is a kind of drawing).
'the line' becomes 'r' (I can't justify this - if you can you should believe this answer much more).
'rule'+'r'='RULER'
'ready to' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ruler that I've seen before include "Graduated straight-edge" , "Aid for a straight line" , "Sovereign, for example" , "Royal" , "One in power" .)