An excellent hardback is always a help (3)
I believe the answer is:
aid
'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" .)