Very bottom drops back in lowest lake (4,3)
I believe the answer is:
dead sea
'lowest lake' is the definition.
(lake below sea level)
'very bottom drops back' is the wordplay.
'very' becomes 'dead' (dead can mean very or absolutely, eg 'dead wrong').
'bottom' becomes 'seat' (synonyms).
'drops back' means to remove the last letter (the back letter is removed).
'seat' with its final letter taken off is 'sea'.
'dead'+'sea'='DEAD SEA'
'in' is the link.
(Other definitions for dead sea that I've seen before include "Disappearing lake" , "Salty lake on the Israel/Jordan border" , "The lake that's a late ocean" , "Inland salt lake on Israel-Jordan border" , "World's lowest lake" .)