It's smart to suggest the southwest is the centre of fashion (5)
I believe the answer is:
swish
'it's smart' is the definition.
(I've seen this before)
'southwest is the centre of fashion' is the wordplay.
'southwest' becomes 'SW' (synonyms).
'the centre of' says to take the centre.
The middle of 'fashion' is 'h'.
'sw'+'is'+'h'='SWISH'
'to suggest the' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for swish that I've seen before include "Extravagant" , "Smart; stylish" , "Elegant" , "Impressively fashionable" , "Smart, fashionable" .)