With two parties involved, bare it all when dancing (9)
I believe the answer is:
bilateral
'with two parties involved' is the definition.
(as in a bilateral agreement)
'bare it all when dancing' is the wordplay.
'when dancing' is an anagram indicator (letters dance around).
'bare'+'it'+'all'='bareitall'
'bareitall' is an anagram of 'BILATERAL'.
(Other definitions for bilateral that I've seen before include "involving two sides" , "Involving two parties" , "Undertaken by two parties" , "Two-sided" , "involving more than one party?" .)