Scientist ordered to abstain initially refused (8)
I believe the answer is:
botanist
'scientist' is the definition.
(I know that botanist is a type of biologist)
'ordered to abstain initially refused' is the wordplay.
'ordered' indicates anagramming the letters.
'initially refused' means to remove the first letter.
'abstain' with its initial letter taken away is 'bstain'.
'to'+'bstain'='tobstain'
'tobstain' anagrammed gives 'BOTANIST'.
(Other definitions for botanist that I've seen before include "Banks" , "Someone studying plants" , "Scientist who studies plants" , "To sit ban out for expert in study of plants" , "Expert in the scientific study of plants" .)