Slow European chopped vegetable in time (10)
I believe the answer is:
decelerate
'slow' is the definition.
(synonyms)
'european chopped vegetable in time' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'chopped' means to remove the last letter.
'vegetable' becomes 'celery' (celery is a kind of vegetable).
'in' indicates putting letters inside.
'time' becomes 'date' (date is a kind of time).
'celery' with its final letter taken off is 'celer'.
'e'+'celer'='eceler'
'eceler' placed inside 'date' is 'DECELERATE'.
(Other definitions for decelerate that I've seen before include "ease up" , "Reduce speed" , "Slow down" , "Move more slowly" .)