Some comprehending downfall (3)
I believe the answer is:
end
'downfall' is the definition.
(I've seen this in another clue)
'some comprehending' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'END' can be found hidden inside 'comprehending'.
(Other definitions for end that I've seen before include "Goal; destruction" , "ambition" , "Extremity" , "Terminus" , "death" .)