Sack lay in hearth (9)
I believe the answer is:
fireplace
'hearth' is the definition.
(I know that hearth can be written as fireplace)
'sack lay' is the wordplay.
'sack' becomes 'fire' (both can mean to dismiss from a job).
'lay' becomes 'place' (I can't explain this - if you can you should believe this answer much more).
'fire'+'place'='FIREPLACE'
'in' is the link.
Can you help me to learn more?
(Other definitions for fireplace that I've seen before include "Domestic chimney opening" , "Hearth" , "Open space at the base of a chimney" , "warm domestic setting" , "Recess at the base of a chimney" .)