Obscure energy cuts end in catastrophe (7)
I believe the answer is:
eclipse
'obscure' is the definition.
(eclipsing is a kind of obscuring)
'energy cuts end in catastrophe' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mcl).
'cuts' becomes 'clips' (clip is a kind of cut**).
'end in' says to take the final letters.
The final letter of 'catastrophe' is 'e'.
'e'+'clips'+'e'='ECLIPSE'
(Other definitions for eclipse that I've seen before include "Black out" , "When one celestial body obscures another" , "concealment" , "blackout" , "screen, more or less" .)