In a mo, the dancing (2,4)
I believe the answer is:
at home
'in' is the definition.
(someone at home is 'in')
'a mo the dancing' is the wordplay.
'dancing' is an anagram indicator.
'mo'+'the'='mothe'
'mothe' anagrammed gives 'thome'.
'a'+'thome'='AT-HOME'
(Other definitions for at home that I've seen before include "celebration" , "Familiar with" , "Reception in one's own abode" , "Comfortable - in one's own country" , "In (for a party?)" .)