Sickly look
I believe the answer is:
pallor
'sickly look' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pallor that I've seen before include "Ashen complexion due to illness" , "showing whiteness" , "Paleness of complexion" , "Whiteness of face as from illness" , "Unnatural lack of colour in the skin" .)