Gas power almost failed — almost (5)
I believe the answer is:
argon
'gas' is the definition.
(I've seen this before)
'power almost failed almost' is the wordplay.
'power almost' becomes 'ar' (I am not sure about this - if you are sure you should believe this answer much more).
'failed' becomes 'gone' ('go' can be a synonym of 'fail').
'almost' means to remove the last letter (most of the word but not all of it).
'gone' with its last letter removed is 'gon'.
'ar'+'gon'='ARGON'
Can you help me to learn more?
(Other definitions for argon that I've seen before include "rare gas" , "elementary" , "Noble gas, Ar" , "Gas used in electric lights" , "Noble gas used in light bulbs" .)