Stop white ant swallowing sodium (9)
I believe the answer is:
terminate
'stop' is the definition.
(terminate can mean to stop or bring to an end)
'white ant swallowing sodium' is the wordplay.
'white ant' becomes 'termite' (synonyms).
'swallowing' is an insertion indicator.
'sodium' becomes 'NA' (Na is the chemical symbol for sodium).
'termite' placed around 'na' is 'TERMINATE'.
(Other definitions for terminate that I've seen before include "Kill off" , "Finalise" , "Put an end to, discontinue" , "Cut short" , "Put an end to, finish" .)