Rank: one he and discontented colonel reviewed (7)
I believe the answer is:
echelon
'rank' is the definition.
(I know that echelon is a type of rank)
'one he and discontented colonel reviewed' is the wordplay.
'and' says to put letters next to each other.
'discontented' says to hollow out the word (remove centre letters) (the word's contents are removed).
'reviewed' is an anagram indicator (letters reviewed or revised).
'colonel' with its middle removed is 'cl'.
'one'+'he'='onehe'
'onehe' put after 'cl' is 'clonehe'.
'clonehe' is an anagram of 'ECHELON'.
(Other definitions for echelon that I've seen before include "Tier" , "Military stepped formation" , "Echo Len (anag.)" , "Leech on (anag.)" , "Ladder formation" .)