Only partly pressed their one demand (6)
I believe the answer is:
ironed
'only' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'partly pressed their one demand' is the wordplay.
'partly' says the answer is hidden in the clue (part of the clue is used).
'IRONED' can be found hidden inside 'pressed their one demand'.
Can you help me to learn more?
(Other definitions for ironed that I've seen before include "Removed creases" , "Smoothed the cloth with heat" , "Smoothed out wrinkles" , "Given a press" , "De Niro (anag)" .)