A right turn-off: stomach botanic garden (9)
I believe the answer is:
arboretum
'botanic garden' is the definition.
(I've seen this before)
'a right turn-off stomach' is the wordplay.
'a right' becomes 'ar' (I've seen this in other clues).
'turn off' becomes 'bore' (I've seen this in another clue).
'stomach' becomes 'tum' (synonyms).
'ar'+'bore'+'tum'='ARBORETUM'
(Other definitions for arboretum that I've seen before include "Collection of elders, say" , "Botanical tree garden" , "Garden where trees and shrubs are cultivated" , "Botanical garden of trees" , "area with great growth" .)