Jeopardise a conclusion by impassioned feelings (8)
I believe the answer is:
endanger
'jeopardise' is the definition.
(synonyms)
'a conclusion by impassioned feelings' is the wordplay.
'a conclusion' becomes 'end' (something's conclusion is its end).
'by impassioned feelings' becomes 'anger' (I can't explain this - if you can you should believe this answer much more).
'end'+'anger'='ENDANGER'
Can you help me to learn more?
(Other definitions for endanger that I've seen before include "Imperil" , "Expose to injury or extinction" , "Put in peril" , "Pose a threat to" , "Put in harm's way" .)