Ultimate use of salt (4)
I believe the answer is:
last
'ultimate' is the definition.
(similar in meaning)
'use of salt' is the wordplay.
'use of' indicates anagramming the letters.
'salt' with letters rearranged gives 'LAST'.
(Other definitions for last that I've seen before include "Latest" , "part of Oxford's restoration with this?" , "Final; keep going" , "Cobbler's model shape" , "model of repair" .)