Silly Superman ran out of froth (5)
I believe the answer is:
spume
'froth' is the definition.
(spume is a kind of froth)
'silly superman ran out' is the wordplay.
'silly' is an anagram indicator.
'out' is a deletion indicator.
'superman' with 'ran' taken out is 'supem'.
'supem' is an anagram of 'SPUME'.
'of' is the link.
(Other definitions for spume that I've seen before include "Froth on waves" , "Sea foam, froth" , "Foam on waves" , "Surf" .)