Apollo's sister raised first-class absinthe (9)
I believe the answer is:
artemisia
'absinthe' is the definition.
The answer and definition can be both plants as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'apollo's sister raised first-class' is the wordplay.
'apollo's sister' becomes 'artemis' (I've seen this in another clue).
'raised' says the letters should be written backwards (going up in a down clue).
'first class' becomes 'ai' (A1 - top quality).
'ai' written backwards gives 'ia'.
'artemis'+'ia'='ARTEMISIA'
Can you help me to learn more?
(Other definitions for artemisia that I've seen before include "Source of malaria drug" , "Flower" , "Aromatic plant related to wormwood" , "herbaceous plant" , "Bitter tasting plant" .)