Small quantities of heroin shifted in lofty settings (7)
I believe the answer is:
eighths
'heroin shifted in lofty settings' is the definition.
I can't judge whether this definition defines the answer.
'small quantities' is the wordplay.
'small' becomes 'eight' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'quantities' becomes 'Hs' (H is an example).
'eight'+'hs'='EIGHTHS'
'of' is the link.
Can you help me to learn more?
(Other definitions for eighths that I've seen before include "Parts of division" , "Half quarters" , "Fractions of 12? per cent" .)
