Firms the leaves that wilt when no longer fresh (3)
I believe the answer is:
cos
This could be a double definition.
'firms' is the first definition.
(co is short for company - a business or firm)
'leaves that wilt when no longer fresh' is the second definition.
'cos' can be an answer for 'leaves' (cos lettuce leaves). I am not certain of the rest of the definition.
'the' acts as a link.
Can you help me to learn more?
(Other definitions for cos that I've seen before include "Variety of lettuce" , "vegetable?" , "often associated with sin" , "leaves > function" , "Mozart fidelity-test opera" .)