One to support stocking revolutionary American poet (9)
I believe the answer is:
suspender
'one to support stocking' is the definition.
'revolutionary american poet' is the wordplay.
'revolutionary' shows that the letters should be reversed in order.
'american' becomes 'us'.
'poet' becomes 'spender' (Stephen Spender**).
'us' in reverse letter order is 'su'.
'su'+'spender'='SUSPENDER'
(Other definitions for suspender that I've seen before include "One responsible for hold-up" , "Sock support" , "Strap to hold up a stocking" , "It upholds" , "hangman?" .)