Unavailing suggestion for economy (7)

I believe the answer is:

useless

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'unavailing' is the definition.
(similar in meaning)

I don't understand the remainder of the clue.

(Other definitions for useless that I've seen before include "Ineffective" , "Not worth a jot" , "Without purpose" , "Lacking in purpose" , "Good-for-nothing" .)

I've seen this clue in The Irish Independent, The Irish News and The Globe and Mail.

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