VAT reduction in train (3)
I believe the answer is:
tub
'vat' is the definition.
(synonyms)
'reduction in train' is the wordplay.
'reduction in' means to remove the last letter (the number of letters in the word is reduced).
'train' becomes 'tube' (tube is a type of subway train).
'tube' with its final letter taken away is 'TUB'.
(Other definitions for tub that I've seen before include "What one ranting thumps" , "Large open vessel" , "Unwieldy boat" , "Container for yogurt, ice-cream" , "subject of Jonson's tale" .)