Second wife ultimately better locked up (7)
I believe the answer is:
secured
'locked up' is the definition.
(I've seen this before)
'second wife ultimately better' is the wordplay.
'second' becomes 's' (common abbreviation).
'ultimately' says to take the final letters.
'better' becomes 'cured' (after being sick).
The last letter of 'wife' is 'e'.
's'+'e'+'cured'='SECURED'
(Other definitions for secured that I've seen before include "Tethered" , "Made safe or fastened safely" , "Made firm" , "Got by special effort" , "Apprehended" .)