Be mournful when member is in middle of speech (7)
I believe the answer is:
elegise
'be mournful' is the definition.
'member is in middle of speech' is the wordplay.
'member' becomes 'leg' (member can mean a limb).
'in' indicates putting letters inside.
'middle of' means to look at the middle letters.
The centre of 'speech' is 'ee'.
'leg'+'is'='legis'
'legis' put into 'ee' is 'ELEGISE'.
'when' acts as a link.
(Other definitions for elegise that I've seen before include "To write a funeral song" , "Write mournfully" .)