Mean, ordering single plant (7)
I believe the answer is:
anemone
'plant' is the definition.
(anemone is a kind of plant)
'mean ordering single' is the wordplay.
'ordering' is an anagram indicator.
'single' becomes 'one' (a single thing - only one).
'mean' with letters rearranged gives 'anem'.
'anem'+'one'='ANEMONE'
(Other definitions for anemone that I've seen before include "Flowering plant - mean one (anag)" , "Pretty flower or sea animal" , "Brightly coloured flower or tube-shaped sea creature" , "Woodland plant - name one (anag)" , "White woodland flower" .)