Mother's broken flask (7)

I believe the answer is:

thermos

'flask' is the definition.
(thermos is a kind of flask)

'mother's broken' is the wordplay.
'broken' indicates an anagram.
'mothers' is an anagram of 'THERMOS'.

(Other definitions for thermos that I've seen before include "Flask trade mark" , "Vacuum flask for mothers" , "Container to retain heat" , "Heat-retaining flask for mothers" .)

I've seen this clue in The Guardian and The Globe and Mail.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.