Partly reverse decision to decorate cake (3)
I believe the answer is:
ice
'decorate cake' is the definition.
'ice' can be an answer for 'decorate' (to ice a cake is to decorate it). I am not certain of the 'cake' bit.
'partly reverse decision to' is the wordplay.
'reverse' says the letters should be written backwards.
'partly' says the answer is hidden in the clue (part of the clue is used).
'eci' is hidden in the letters of 'decision to'.
'eci' back-to-front is 'ICE'.
Can you help me to learn more?
(Other definitions for ice that I've seen before include "Chill - harden" , "Skating surface" , "A state of water" , "Slippery surface" , "If it's thin, skating on it can be dangerous" .)