"This Is the Life" singer Macdonald (3)
I believe the answer is:
amy
'this is the life singer macdonald' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amy that I've seen before include "Girl" , "so-called little woman" , "lady" , "-- Johnson, female flyer" , "- Johnson, Eng. aviatrix" .)