Picked up passenger OK (4)
I believe the answer is:
fair
'ok' is the definition.
(thesaurus)
'picked up passenger' is the wordplay.
'picked up' shows a homophone (sound like).
'passenger' becomes 'fare' (fare is a kind of passenger).
'fare' is a homophone of 'FAIR'.
(Other definitions for fair that I've seen before include "here for the ride?" , "Just; fete" , "Traders' gathering" , "Market for the sale of produce" , "promotional exhibition" .)