Drink some sentimental octogenarian knocked over (4)
I believe the answer is:
cola
'drink' is the definition.
(cola is a type of drink)
'some sentimental octogenarian knocked over' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'knocked over' shows that the letters should be reversed in order.
'aloc' can be found hidden inside 'sentimental octogenarian'.
'aloc' reversed gives 'COLA'.
(Other definitions for cola that I've seen before include "Carbonated soft drink" , "Fizzy drink" , "pop" , "Cold drink" .)