Muscle and bravado initially overturning new conflict (5)
I believe the answer is:
brawn
'muscle' is the definition.
(I know that muscle can be written as brawn)
'bravado initially overturning new conflict' is the wordplay.
'initially' suggests taking the first letters.
'overturning' says the letters should be written backwards.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'conflict' becomes 'war' (war is a kind of conflict).
The first letter of 'bravado' is 'b'.
'n'+'war'='nwar'
'nwar' back-to-front is 'rawn'.
'b'+'rawn'='BRAWN'
'and' is the link.
(Other definitions for brawn that I've seen before include "Muscularity" , "Beefiness" , "Muscle; strength" , "Physical strength; cooked meat" , "Strength; a jellied loaf" .)