Possibly lack bite as formal dress (5,3)
I believe the answer is:
black tie
'formal dress' is the definition.
'black tie' can be an answer for 'dress' (black tie is a kind of dress). I'm not certain of the 'formal' bit.
'possibly lack bite' is the wordplay.
'possibly' indicates anagramming the letters.
'lack'+'bite'='lackbite'
'lackbite' is an anagram of 'BLACK-TIE'.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for black tie that I've seen before include "Accompaniment of 11" , "Formal evening wear for men" , "Formal attire" , "It's worn with a dinner jacket" , "expensive party-going habit" .)