Downs first drink from cask (4)
I believe the answer is:
drum
'cask' is the definition.
(thesaurus)
'downs first drink' is the wordplay.
'first' suggests taking the first letters.
'drink' becomes 'rum' (rum is a kind of drink).
The first letter of 'downs' is 'd'.
'd'+'rum'='DRUM'
'from' acts as a link.
(Other definitions for drum that I've seen before include "See 16" , "- Taps (Walt Whitman)" , "house" , "rap" , "Empty" .)