Rank of Iron Duke, holding appeal up (5)
I believe the answer is:
fetid
'rank' is the definition.
(I've seen this in another clue)
'iron duke holding appeal up' is the wordplay.
'iron' becomes 'fe' (chemical symbol for iron).
'duke' becomes 'd' (abbreviation).
'holding' means one lot of letters go next to another.
'appeal' becomes 'it' ('it' can mean something attractive or appealing).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'd'+'it'='dit'
'dit' written backwards gives 'tid'.
'fe'+'tid'='FETID'
'of' is the link.
(Other definitions for fetid that I've seen before include "Stinking, like animal breath" , "Stinking, rank" , "Evil-smelling, stinking" , "Smelly through decay" , "Putrid, malodorous" .)