Multiply a drink (6)
This clue is a double definition.
'multiply' is the first definition.
(I know that treble is a more specific form of the action multiply)
'a drink' is the second definition.
(Other definitions for treble that I've seen before include "High voice; occurring three times" , "High-frequency (radio control knob)" , "High darts score" , "high frequency" , "Threefold; boy's voice" .)
But I've got no explanation for this one! Could you help me understand?
(Other definitions for double that I've seen before include "Dead ringer" , "Twice - bent over - run" , "Offence of leaving one's car where it blocks another" , "Ringer - large drink" , "Second charge for the same offence" .)