Word puzzle on coach (5)
I believe the answer is:
rebus
'word puzzle' is the definition.
(I've seen this before)
'on coach' is the wordplay.
'on' becomes 're' (regarding).
'coach' becomes 'bus' (synonyms).
're'+'bus'='REBUS'
(Other definitions for rebus that I've seen before include "that's puzzling" , "Puzzle consisting of pictures representing syllables and words" , "solver?" , "Puzzling device" , "Visual type of word puzzle" .)