More certain about right conclusion, but give in (9)
I believe the answer is:
surrender
'give in' is the definition.
(thesaurus)
'more certain about right conclusion' is the wordplay.
'more certain' becomes 'surer' ('sure' can be a synonym of 'certain').
'about' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'conclusion' becomes 'end' (end is a kind of conclusion**).
'r'+'end'='rend'
'surer' going around 'rend' is 'SURRENDER'.
'but' is the link.
(Other definitions for surrender that I've seen before include "Yield - release" , "Submit (to an opponent)" , "Yield, give in" , "Yield to the control of another" , "Capitulation" .)