I'm getting round America on board stock car (9)
I believe the answer is:
limousine
'car' is the definition.
(limousine is a kind of car)
'i'm getting round america on board stock' is the wordplay.
I cannot quite understand how this works, but
'i'm' could be 'im' and 'im' is found within the answer.
'round' could be 'o' (round can mean a round object) and 'o' is found within the answer.
'america' could be 'us' (United States) and 'us' is found within the answer.
'stock' could be 'line' (synonyms) and 'line' is found in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
(Other definitions for limousine that I've seen before include "Large luxurious car" , "Luxury car" , "Form of transport" , "Luxurious car (with a chauffeur?)" , "big car" .)