Prison accommodates large family (4)
I believe the answer is:
clan
'family' is the definition.
(I know that clan is a type of family)
'prison accommodates large' is the wordplay.
'prison' becomes 'can' (the can is American slang for prison).
'accommodates' is an insertion indicator.
'large' becomes 'L' (eg in clothes sizes).
'can' enclosing 'l' is 'CLAN'.
(Other definitions for clan that I've seen before include "Kinship group" , "Tribal family" , "Scottish family grouping" , "Group with a tartan?" , "Tribe or collection of families under a cheiftain" .)