Costume from Peru finally back in fashion (7)
I believe the answer is:
uniform
'costume' is the definition.
(both can mean clothing)
'peru finally back in fashion' is the wordplay.
'finally' says to take the final letters.
'back' says the letters should be written in reverse.
'fashion' becomes 'form' (both can mean to shape something for a purpose).
The last letter of 'peru' is 'u'.
'in' in reverse letter order is 'ni'.
'u'+'ni'+'form'='UNIFORM'
'from' acts as a link.
(Other definitions for uniform that I've seen before include "Regular - formal dress" , "The clothing is always the same," , "Military clothes" , "Comms code for U" , "Flat" .)