Crossword Genius

Draw a line under the law? (4)

Ross

I believe the answer is:

rule

I'm a little stuck... Click here to teach me more about this clue!

'the law?' is the definition.
(law is a kind of rule)

'draw a line under' is the wordplay.
I cannot really understand how this works, but
'line' could be 'l' (used when specifying particular lines from a poem) and 'l' is found in the answer.
The remaining letters 'rue' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for rule that I've seen before include "Determination" , "line to be followed" , "Strip" , "Exercise authority over" , "Standard" .)

I've seen this clue in the Sydney Morning Herald.
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