Shelter a year in overcrowded neighbourhood (6)
I believe the answer is:
asylum
'shelter' is the definition.
(asylum is a kind of shelter)
'a year in overcrowded neighbourhood' is the wordplay.
'year' becomes 'y'.
'in' is an insertion indicator.
'overcrowded neighbourhood' becomes 'slum'.
'y' placed within 'slum' is 'sylum'.
'a'+'sylum'='ASYLUM'
(Other definitions for asylum that I've seen before include "A shelter from danger or hardship" , "Place of safety or protection" , "Shelter for refugees" , "Refugee's protection" , "Shelter given to refugee" .)