Long thrifty arrangement occurs regularly (11)

I believe the answer is:

fortnightly

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'occurs regularly' is the definition.
I can't tell whether this definition defines the answer.

'long thrifty arrangement' is the wordplay.
'arrangement' indicates anagramming the letters.
'long'+'thrifty'='longthrifty'
'longthrifty' with letters rearranged gives 'FORTNIGHTLY'.

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(Other definitions for fortnightly that I've seen before include "Every fourteen days" , "Every two weeks" , "at regular intervals" .)

I've seen this clue in The Mirror.

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