Cask in pub on lake (6)
I believe the answer is:
barrel
'cask' is the definition.
(synonyms)
'pub on lake' is the wordplay.
'pub' becomes 'bar' (both are drinking establishments).
'on' becomes 're' ('on' can be mean 'with reference to').
'lake' becomes 'l' (geographical abbreviation).
'bar'+'re'+'l'='BARREL'
'in' acts as a link.
(Other definitions for barrel that I've seen before include "Tun" , "Round wooden cask made by cooper" , "Beer cask" , "''Roll out the ..., let's have a ... of fun'' (WWII song)" , "Cylindrical crate" .)