A little added in rush (4)
I believe the answer is:
dash
This clue is a double definition.
'a little added' is the first definition.
(eg a dash of sauce)
'rush' is the second definition.
(dashing is a kind of rushing)
'in' is the link.
(Other definitions for dash that I've seen before include "Run fast with flair" , "style" , "Short race run at top speed" , "scotch" , "Hurry ("must ____!")" .)