Friendly wife, member (4)
I believe the answer is:
warm
'friendly' is the definition.
('warm' is associated in meaning with 'friendly')
'wife member' is the wordplay.
'wife' becomes 'w'.
'member' becomes 'arm' (arm is a kind of member**).
'w'+'arm'='WARM'
(Other definitions for warm that I've seen before include "easily aroused" , "Heated; enthusiastic" , "showing enthusiasm" , "Affectionate; quite hot" , "Pleasantly hot" .)