Walk on board cool craft (9)
I believe the answer is:
spaceship
'craft' is the definition.
(spaceship is a kind of craft)
'walk on board cool' is the wordplay.
I cannot really see how this works, but
'walk' could be 'pace' (pacing is a kind of walking) and 'pace' is present in the answer.
'cool' could be 'hip' (hip can mean cool or fashionable) and 'hip' is present in the answer.
'on board' could be 'ss' (I've seen this in other clues) and 'ss' is located in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for spaceship that I've seen before include "Transport that's out of this world" , "orbiter, perhaps" , "craft going far?" , "Interplanetary craft" , "long-distance vessel" .)