Once, Hell almost created this level (7)
I believe the answer is:
echelon
'this level' is the definition.
(I've seen this in another clue)
'once hell almost created' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'created' indicates anagramming the letters (I've seen 'create' mean this).
'once'+'hell'='oncehell'
'oncehell' with its final letter removed is 'oncehel'.
'oncehel' is an anagram of 'ECHELON'.
(Other definitions for echelon that I've seen before include "Staggering display of military" , "Military stepped formation" , "Military row formation" , "position in society" , "series of steps" .)