Saint hugs large plant in thoroughfare (6)
I believe the answer is:
street
'thoroughfare' is the definition.
(street is a kind of thoroughfare)
'saint hugs large plant' is the wordplay.
'saint' becomes 'st'.
'hugs' is an insertion indicator.
'large plant' becomes 'tree' (I've seen this before).
'st' going around 'tree' is 'STREET'.
'in' is the link.
(Other definitions for street that I've seen before include "Perry's Della" , "Part of motorist's route" , "Built-up road" , "- Arab; - light" , "Tester in public road" .)