Rank slipping on leech! (7)
I believe the answer is:
echelon
'rank' is the definition.
(I've seen this in another clue)
'slipping on leech' is the wordplay.
'slipping' indicates anagramming the letters.
'on'+'leech'='onleech'
'onleech' with letters rearranged gives 'ECHELON'.
(Other definitions for echelon that I've seen before include "Rank - status" , "Level or rank in an organisation" , "Wedge-shaped formation of troops" , "Level of people in organisation" , "Level of command" .)