It makes a straight line for monarch (5)

I believe the answer is:

ruler

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'it' is the definition.
The definition suggests a singular noun which matches the answer.

'a straight line for monarch' is the wordplay.
'a straight line' becomes 'rule' (I've seen this in another clue).
'for' says to put letters next to each other.
'monarch' becomes 'R' (abbreviation for regina, e.g. in ER ).
'rule'+'r'='RULER'

'makes' is the link.

Can you help me to learn more?

(Other definitions for ruler that I've seen before include "king perhaps" , "Chief" , "Sovereign - support for a firm line!" , "One governing" , "Monarch - drafting tool" .)

I've seen this clue in The Mirror.

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