Gathered together, dressed up as dames (7)
I believe the answer is:
amassed
'gathered together' is the definition.
(I've seen this before)
'dressed up as dames' is the wordplay.
'dressed up' is an anagram indicator.
'as'+'dames'='asdames'
'asdames' anagrammed gives 'AMASSED'.
(Other definitions for amassed that I've seen before include "Gathered together" , "Got up" , "Mad seas (anag.)" , "Accumulated, gathered" , "Accumulated, piled up" .)