Crossword Genius

An excellent hardback is always a help (3)

Ross

I believe the answer is:

aid

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

'help' is the definition.
(synonyms)

'an excellent hardback is always a' is the wordplay.
I cannot really see how this works, but
'an' could be 'i' (Roman numeral for one) and 'i' is present in the answer.
'a' is present in the answer.
A single letter 'd' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for aid that I've seen before include "Help. Assist" , "Relief" , "Help or succour" , "Good point" , "A hand" .)

I've seen this clue in the Evening Standard.
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