Let loose dress down, inferior to large one (8)
I believe the answer is:
liberate
'let loose' is the definition.
(thesaurus)
'dress down inferior to large one' is the wordplay.
'dress down' becomes 'berate' (synonyms).
'inferior to' says to put letters next to each other (in a down clue, some letters go below others).
'large' becomes 'L' (eg in clothes sizes).
'one' becomes 'i' (Roman numeral).
'l'+'i'='li'
'berate' put after 'li' is 'LIBERATE'.
(Other definitions for liberate that I've seen before include "Set free, release from slavery" , "Set free, as from oppressive authority" , "Free (someone)" , "let go" , "Make free" .)