Vagrant ingredient of egg-white (3)
I believe the answer is:
bum
'vagrant' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for bum that I've seen before include "Cadge" , "American hobo or English bottom" , "American tramp or English bottom" , "US tramp" , "Begging" .)