Crossword Genius

Unhelpful instruction for conserving something? (7)

Ross

I believe the answer is:

useless

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

I can't explain the rest of the clue.

(Other definitions for useless that I've seen before include "Vain - unavailing" , "Unemployable" , "to no avail" , "Not worth a jot" , "Vain, impractical" .)

I've seen this clue in The Times.
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