The term "mealy wing" refers to a condition most commonly observed in birds when their wings become flimsy, weak and pale due to improper nutrition. The use of this phrase is quite limited, and there aren't many synonyms for it in general usage. However, some words that come to mind are "pallid wing", "anaemic wing", and "undernourished wing". These terms all carry the connotation of weakness and malnourishment that is commonly observed in birds suffering from mealy wing syndrome. Other possibilities include "flaccid wing", "pale wing" or "decrepit wing", depending on the specific context in which the term is being used.