Pedestrian jazz performer left out and replaced by King (6)
I believe the answer is:
walker
'pedestrian' is the definition.
(synonyms)
'jazz performer left out and replaced by king' is the wordplay.
I cannot quite see how this works, but
'left' could be 'al' (I've seen this in other clues) and 'al' is present in the answer.
'king' could be 'er' (abbreviation for Edward Rex, various English kings) and 'er' is located in the answer.
This explanation may well be incorrect...
(Other definitions for walker that I've seen before include "One going on foot" , "Pedestrian" , "Rambler" .)