Trendy to guide to roundabout (8)
I believe the answer is:
indirect
'roundabout' is the definition.
('indirect' can be similar in meaning to 'roundabout')
'trendy to guide' is the wordplay.
'trendy' becomes 'in'.
'to guide' becomes 'direct' ('direct' can be a synonym of 'guide').
'in'+'direct'='INDIRECT'
'to' acts as a link.
(Other definitions for indirect that I've seen before include "Oblique, not straight" , "(Of tax) levied on goods rather than income" , "Neither straight or straightforward" , "In credit, not being straight" , "In credit (anag.)" .)