A confident walk catching on with a spaceman (9)
I believe the answer is:
astronaut
'spaceman' is the definition.
(synonyms)
'a confident walk catching on with a' is the wordplay.
'confident walk' becomes 'strut'.
'catching' indicates putting letters inside.
'with' is a charade indicator (letters next to each other).
'on'+'a'='ona'
'strut' enclosing 'ona' is 'stronaut'.
'a'+'stronaut'='ASTRONAUT'
(Other definitions for astronaut that I've seen before include "Armstrong or Sharman, say" , "High-flyer" , "Buzz Aldrin, for example" , "spaceman" , "Buzz Aldrin, e.g." .)