A firm imports chopped vegetable with increasing speed (11)
I believe the answer is:
accelerando
'increasing speed' is the definition.
(musical term)
'a firm imports chopped vegetable with' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'imports' means one lot of letters goes inside another.
'chopped' means to remove the last letter.
'vegetable' becomes 'celery' (celery is a kind of vegetable).
'with' becomes 'and'.
'celery' with its last letter taken off is 'celer'.
'celer'+'and'='celerand'
'co' enclosing 'celerand' is 'ccelerando'.
'a'+'ccelerando'='ACCELERANDO'
(Other definitions for accelerando that I've seen before include "Gradually increasing in speed (mus.)" , "Getting gradually faster" , "going faster and faster" , "Speeding up (music)" , "faster passage" .)