Drink last in flask in wood (4)
I believe the answer is:
teak
'wood' is the definition.
(teak is a kind of wood)
'drink last in flask' is the wordplay.
'drink' becomes 'tea' (tea is a kind of drink).
'last in' says to take the final letters.
The final letter of 'flask' is 'k'.
'tea'+'k'='TEAK'
'in' acts as a link.
(Other definitions for teak that I've seen before include "Type of tree" , "Hard durable timber" , "Indian hardwood" , "Strong heavy wood of an Asian tree" , "E. Indies hardwood" .)