Before noon cut flower (6)
I believe the answer is:
severn
'flower' is the definition.
(River Severn)
'before noon cut' is the wordplay.
'before' says to put letters next to each other.
'noon' becomes 'n' (abbreviation for noon).
'cut' becomes 'sever' (to sever is to cut or split).
'n' after 'sever' is 'SEVERN'.
(Other definitions for severn that I've seen before include "Flower" , "GB's longest river" , "Shrewsbury's river" , "Major UK river" , "Welsh and English river" .)