Sure about lieutenant, in the end (6)
I believe the answer is:
result
'the end' is the definition.
(I've seen this in another clue)
'sure about lieutenant' is the wordplay.
'about' indicates anagramming the letters.
'lieutenant' becomes 'lt' (abbreviation for lieutenant).
'sure' with letters rearranged gives 'resu'.
'resu'+'lt'='RESULT'
'in' is the link.
(Other definitions for result that I've seen before include "Ulster (anag) - outcome" , "End - issue" , "Effect of lustre" , "Outcome of an undertaking" , "Verdict" .)