Flower one gentleman picked up (4)
I believe the answer is:
iris
'flower' is the definition.
(thesaurus)
'one gentleman picked up' is the wordplay.
'one' becomes 'i' (Roman numeral**).
'gentleman' becomes 'sir' (I've seen this before).
'picked up' is a reversal indicator.
'sir' reversed gives 'ris'.
'i'+'ris'='IRIS'
(Other definitions for iris that I've seen before include "Fleur-de-lis" , "Murdoch in writing" , "is 21[WOMAN], perhaps" , "--- Murdoch, author" , "Ms Murdoch" .)