Notice habitual junkie Holmes is finally clean (8)
I believe the answer is:
spotless
'clean' is the definition.
(similar in meaning)
'notice habitual junkie holmes is finally' is the wordplay.
'notice' becomes 'spot' (spot can mean to notice or observe).
'finally' indicates one should take the final letters.
The last letters of 'habitual junkie holmes is' are 'less'.
'spot'+'less'='SPOTLESS'
(Other definitions for spotless that I've seen before include "honest!" , "Without a mark, completely clean" , "free from sin" , "Absolutely pure, clean" , "showing no sign of acne?" .)