Graduate doctor loves woody grass (6)
I believe the answer is:
bamboo
'woody grass' is the definition.
(I've seen this before)
'graduate doctor loves' is the wordplay.
'graduate' becomes 'BA' (someone with a Bachelor of Arts degree).
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'loves' becomes 'oo' (love means 0 in tennis).
'ba'+'mb'+'oo'='BAMBOO'
(Other definitions for bamboo that I've seen before include "Heavy tropical cane used in furniture" , "Treelike tropical grass" , "Spotted tile; carnival mask" , "Woody grass plant" , "Tropical grass/wood" .)