Trade vehicle held in on tracks (9)
I believe the answer is:
carpentry
'trade' is the definition.
(carpentry is a kind of trade)
'vehicle held in on tracks' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'held in' becomes 'pent' (I've seen this in another clue).
'on' means one lot of letters go next to another.
'tracks' becomes 'RY' (abbreviation for railway).
'car'+'pent'+'ry'='CARPENTRY'
(Other definitions for carpentry that I've seen before include "Manipulating deal, perhaps" , "part of building" , "Woodwork" , "Woodworking" , "The purpose of chips" .)