A large pest keeps quiet in poor accommodation (9)
I believe the answer is:
almshouse
'poor accommodation' is the definition.
(historical type of accommodation for the poor)
'a large pest keeps quiet' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'pest' becomes 'mouse' (mice may be considered pests).
'keeps' is an insertion indicator.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'mouse' enclosing 'sh' is 'mshouse'.
'a'+'l'+'mshouse'='ALMSHOUSE'
'in' is the link.
(Other definitions for almshouse that I've seen before include "Place for poor" , "dwelling for an old woman?" , "Shelter charitably provided" , "Accommodation for the needy" , "Old folks' home (once)" .)