Chamber is consequently filled by island lake (4)
I believe the answer is:
silo
'chamber' is the definition.
(chamber holding a missile)
'consequently filled by island lake' is the wordplay.
'consequently' becomes 'so' (synonyms).
'filled by' indicates putting letters inside.
'island' becomes 'i'.
'lake' becomes 'l' (geographical abbreviation).
'i'+'l'='il'
'so' placed around 'il' is 'SILO'.
'is' acts as a link.
(Other definitions for silo that I've seen before include "Grain storage area" , "Tower for making fodder" , "Launch site" , "Grain store; missile site" , "Large container for oils" .)