Cold thug shows muscle (5)
I believe the answer is:
clout
'muscle' is the definition.
(I have seen 'political muscle' mean 'clout' so perhaps 'muscle' could also mean 'clout')
'cold thug' is the wordplay.
'cold' becomes 'c' (eg on taps).
'thug' becomes 'lout'.
'c'+'lout'='CLOUT'
'shows' is the link.
(Other definitions for clout that I've seen before include "Lay one on" , "strike" , "Old-fashioned garment" , "Cuff" , "piece of clothing" .)