Standard cut for root vegetable (7)
I believe the answer is:
parsnip
'root vegetable' is the definition.
(parsnip is a kind of root vegetable)
'standard cut' is the wordplay.
'standard' becomes 'par' (I've seen this before).
'cut' becomes 'snip' (snipping is a kind of cutting).
'par'+'snip'='PARSNIP'
'for' is the link.
(Other definitions for parsnip that I've seen before include "Yellow root vegetable" , "A white root vegetable" , "Sweet root vegetable" , "food" , "Plant with edible white root" .)