Substance got him dancing in swimwear (7,8)
I believe the answer is:
Here is my best explanation:
'swimwear' is the definition.
I can't tell whether this defines the answer.
'substance got him dancing' is the wordplay.
'dancing' indicates anagramming the letters.
'substancegothim' is an anagram of 'BATHING COSTUMES'.
'in' acts as a link.