We are equal, adopting very successful formal dress (5,3)
I believe the answer is:
white tie
'dress' is the definition.
(white tie is a kind of dress)
'we are equal adopting very successful formal' is the wordplay.
I cannot really understand how this works, but
'equal' could be 'tie' (tying is a kind of equaling) and 'tie' is found within the answer.
'successful' could be 'hit' (I've seen this in another clue) and 'hit' is located in the answer.
'we' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for white tie that I've seen before include "Like formal do" , "Part of formal attire" , "Formal dress code" , "Men's formal dress" , "Full evening dress for men" .)