Usage: 2 forms in 2 verses
Form Translated As     In Verse(s)
πτερυσσόμεναι flapping LXX.Ezek.1.23
πτερυσσομένων flapping LXX.Ezek.3.13

Liddell-Scott-Jones

πτερύσσομαι (pterussomai) to flap wings G:V

πτερύσσομαι,

Attic dialect πτερύττομαι, future πτερύξομαι, flutter, flap the wings like a cock crowing, [Refs 2nd c.AD+]; ἐπτερύσσετο should perhaps be restored for ἀπτ- in [Refs 7th c.BC+]

__II metaphorically, triumph, exult, [Refs 4th c.BC+]
__II.2 become full-fledged, spread one's wings for flight, of the soul, [Refs 1st c.AD+]