Air gently moving piece of cake (6)
I believe the answer is:
breeze
'piece of cake' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for breeze that I've seen before include "Kind of block" , "Light wind or small cinders" , "Soft air" , "The building block is light" , "Gust" .)