At first, bus permits can be excellent (6)
I believe the answer is:
superb
'be excellent' is the definition.
(thesaurus)
'at first bus' is the wordplay.
'at' becomes 'super' (I can't justify this - if you can you should give a lot more credence to this answer).
'first' indicates taking the first letters.
The first letter of 'bus' is 'b'.
'super'+'b'='SUPERB'
'permits can' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for superb that I've seen before include "Dazzling" , "'Excellent, brilliant (6)'" , "Brilliant, fantastic" , "Magnificent, quite splendid" , "Splendid, brilliant" .)