Light wind, that's easy (6)
I believe the answer is:
breeze
I believe this is a double definition.
'light wind' is the first definition.
(a breeze is a wind)
'easy' is the second definition.
(I've seen this before)
'that's' acts as a link.
(Other definitions for breeze that I've seen before include "get the wind up" , "Doddle - light wind" , "Given piece of cake" , "Gentle wind or zephyr" , "Something very easy to do (colloq.)" .)