Wave when female friend returns (4)
I believe the answer is:
flap
'wave' is the definition.
(I know that wave can be written as flap)
'female friend returns' is the wordplay.
'female' becomes 'f' (abbreviation).
'friend' becomes 'pal' (pal can mean a friend).
'returns' says the letters should be written backwards.
'pal' in reverse letter order is 'lap'.
'f'+'lap'='FLAP'
'when' acts as a link.
(Other definitions for flap that I've seen before include "Tab - tizzy - move wings" , "Wave up and down - panic" , "Excitement" , "Adjustable part of wing - panic" , "State of agitation" .)