Flower one gentleman brought up (4)
I believe the answer is:
iris
'flower' is the definition.
(thesaurus)
'one gentleman brought up' is the wordplay.
'one' becomes 'i' (Roman numeral**).
'gentleman' becomes 'sir' (I've seen this before).
'brought up' says the letters should be written backwards (down clues only).
'sir' written backwards gives 'ris'.
'i'+'ris'='IRIS'
(Other definitions for iris that I've seen before include "One controlling pupil' s reactions" , "Rainbow-goddess" , "pupil's governor" , "Flowers in the eye?" , "Coloured part of the lamp" .)