More certain about right conclusion being capitulation (9)
I believe the answer is:
surrender
'being capitulation' is the definition.
(I've seen this before)
'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' (something's conclusion is its end).
'r'+'end'='rend'
'surer' placed around 'rend' is 'SURRENDER'.
(Other definitions for surrender that I've seen before include "Concede" , "Capitulate, relinquish" , "Submit (to an opponent)" , "Cease resistance" , "Yield to the control of another" .)