1
general::
1. In flight, usually referring to a bird as opposed to a plane. For example, Louise is very good at identifying birds on the wing. [Late 1400s] 2. Active, in motion, as in Coaches are always on the wing, trying to recruit talented athletes. This usage may be obsolescent. [c. 1500]
American Heritage Idioms
2
general::
Phrase(s): on the wing
Fig. while flying; while in flight. (Usually refers to birds, fowl, etc., not people or planes.) • There is nothing as pretty as a bird on the wing. • The hawk caught the sparrow on the wing.
McGrawhill's American Idioms And Phrasal Verbs