Being lazy is fairly easy at first (4)
I believe the answer is:
life
'being' is the definition.
(life is a kind of being)
'lazy is fairly easy at first' is the wordplay.
'at first' indicates taking the first letters.
The initial letters of 'lazy is fairly easy' is 'LIFE'.
(Other definitions for life that I've seen before include "The longest sentence" , "Maximum stretch?" , "Actuarial estimate of our remaining years" , "Animation" , "Existence - biography" .)