Thus has a use in pickle (5)
I believe the answer is:
souse
'pickle' is the definition.
(I've seen this in another clue)
'thus has a use' is the wordplay.
'thus' becomes 'so' (synonyms).
'has' says to put letters next to each other.
'so'+'use'='SOUSE'
'in' acts as a link.
(Other definitions for souse that I've seen before include "Drench" , "Duck" , "Wash" , "dip" , "Marinate" .)