Purpose concealed by corrupt union - that's the insinuation (8)
I believe the answer is:
innuendo
'the insinuation' is the definition.
('innuendo' can be a synonym of 'insinuation')
'purpose concealed by corrupt union' is the wordplay.
'purpose' becomes 'end' (I've seen this before).
'concealed by' is an insertion indicator.
'corrupt' indicates anagramming the letters.
'union' with letters rearranged gives 'innuo'.
'end' going inside 'innuo' is 'INNUENDO'.
'that's' is the link.
(Other definitions for innuendo that I've seen before include "Suggestive remark" , "Indirect remark" , "nudge nudge)" , "Malicious insinuation" , "Naughty suggestion" .)