Get on, fix bait inside (6)
I believe the answer is:
obtain
'get' is the definition.
(synonyms)
'on fix bait inside' is the wordplay.
'fix' is an anagram indicator.
'inside' indicates putting letters inside.
'bait' anagrammed gives 'btai'.
'on' enclosing 'btai' is 'OBTAIN'.
(Other definitions for obtain that I've seen before include "Come into possession of" , "'Get, acquire (6)'" , "Gain possession of" , "Take possession of" , "Get or lay hold of" .)