Dark, extremely retro hat (8)
I believe the answer is:
sombrero
'hat' is the definition.
(sombrero is a kind of hat)
'dark extremely retro' is the wordplay.
'dark' becomes 'sombre' (I've seen this before).
'extremely' suggests removing the centre (only the extremes of the word are used).
'retro' with its middle taken out is 'ro'.
'sombre'+'ro'='SOMBRERO'
(Other definitions for sombrero that I've seen before include "Large Mexican sun-hat" , "Hat for South American" , "Covering up" , "Wide-brimmed hat of Mexico" , "One sported in sun" .)