Root we'd seen in southeast (5)
I believe the answer is:
swede
'root' is the definition.
(I know that swede is a type of turnip)
'we'd seen in southeast' is the wordplay.
'seen in' means one lot of letters goes inside another.
'southeast' becomes 'SE' (synonyms).
'wed' inserted within 'se' is 'SWEDE'.
(Other definitions for swede that I've seen before include "Foreigner" , "Scandinavian national" , "Nobel for one" , "Native of Stockholm" , "Man from Malmo" .)