Stunning little number? (8)
I believe the answer is:
narcotic
This clue might be a double definition.
'stunning' is the first definition.
(thesaurus)
'little number?' is the second definition.
'narcotic' can be an answer for 'number?' (I've seen this before). I am not certain of the 'little' bit.
Can you help me to learn more?
(Other definitions for narcotic that I've seen before include "Drug to induce drowsiness or stupor" , "Drug that induces sleep" , "Addictive drug affecting mood or behaviour" , "drug supplied" , "Sedative" .)