Fashionable rental arranged within (8)
I believe the answer is:
internal
'fashionable' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I don't see?
'rental arranged within' is the wordplay.
I cannot quite see how this works, but
an anagram of 'rental' is 'ternal' which is present in the answer.
'within' could be 'in' and 'in' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for internal that I've seen before include "Cause of engine power" , "In-house - private" , "Located inward" , "Inside the body" , "Located inside" .)