She's beginning to litigate on air (5)
I believe the answer is:
aural
'on air' is the definition.
(I know this)
'she's beginning to litigate' is the wordplay.
'she' becomes 'aura' ().
'beginning to' indicates taking the first letters.
The initial letter of 'litigate' is 'l'.
'aura'+'l'='AURAL'
(Other definitions for aural that I've seen before include "To do with hearing or the ears" , "Relating to the hearing organs" , "Pertaining to the ear" , "Relating to sense of hearing" , "of air" .)