Mother's broken the flask (7)
I believe the answer is:
thermos
'flask' is the definition.
(I know that thermos is a type of vacuum bottle)
'mother's broken' is the wordplay.
'broken' indicates an anagram.
'mothers' with letters rearranged gives 'THERMOS'.
'the' acts as a link.
(Other definitions for thermos that I've seen before include "Heat-retaining flask for mothers" , "Vacuum flask for mothers" , "Container to retain heat" , "Flask trade mark" .)