Right in the bottom by a wild horse! (6)
I believe the answer is:
brumby
'a wild horse' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?
'right in the bottom by' is the wordplay.
'right' becomes 'r' (common abbreviation).
'in' is an insertion indicator.
'the bottom' becomes 'bum' (synonyms).
'r' placed into 'bum' is 'brum'.
'brum'+'by'='BRUMBY'
Can you help me to learn more?
(Other definitions for brumby that I've seen before include "One Australian breaks in" , "H [HORSE]" , "Wild horse in Australia" .)