More secure business with monarch (6)

I believe the answer is:

firmer

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'more secure' is the definition.
('firm' can be similar in meaning to 'secure')

I can't explain the rest of the clue.

(Other definitions for firmer that I've seen before include "harder to uproot?" , "More resolute" , "Steadier" , "More rigid" , "not so easy to penetrate?" .)

I've seen this clue in The Times.

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