Finally, thanks about salt being returned (2,4)
I believe the answer is:
at last
'finally' is the definition.
(synonyms)
'thanks about salt being returned' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'about' means one lot of letters goes inside another.
'being returned' says the letters should be written backwards.
'ta' placed around 'salt' is 'tsalta'.
'tsalta' reversed gives 'AT LAST'.
(Other definitions for at last that I've seen before include "working as a cobbler?" , "Finally, after much delay" , "In the end, after much delay" , "Finally, ultimately" , "'In the end (2,4)'" .)