Good public transport system is the ultimate aim (5)
I believe the answer is:
grail
'the ultimate aim' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'good public transport system' is the wordplay.
I cannot really understand how this works, but
'good' could be 'g' (abbreviation) and 'g' is present in the answer.
'transport system' could be 'rail' (I've seen this in another clue) and 'rail' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for grail that I've seen before include "Round Table Knights sought the Holy ....." , "Arthurian knights' quest" , "sought by Parsifal" , "Legendary holy item" , "Cherished goal" .)