Supports what a peacock does (6)
I believe the answer is:
'supports' is the definition.
(strut is a kind of support)
'a peacock does' is the wordplay.
'a peacock' becomes 'strut' (I've seen this before).
'does' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'what' acts as a link.
Can you help me to learn more?
(Other definitions for struts that I've seen before include "Bars inserted into framework to strengthen it" , "Strengthening bars" , "parades with conscious pride" , "Walks proudly like farmyard rooster" , "Walks in proud, showy way" .)