Crossword Genius

To reduce consumption is of no avail (7)

Ross

I believe the answer is:

useless

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

'to reduce consumption is' is the definition.
I can't tell whether this defines the answer.

'no avail' is the wordplay.
I cannot quite see how this works, but
'avail' could be 'use' (I've seen this in another clue) and 'use' is present in the answer.
The remaining letters 'less' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'of' is the link.

Can you help me to learn more?

(Other definitions for useless that I've seen before include "Without purpose" , "Futile and unavailing" , "Lacking in purpose" , "Of no benefit" , "Good for nothing" .)

I've seen this clue in The Globe and Mail.
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