Shelter unknown number in a favela (6)
I believe the answer is:
asylum
'shelter' is the definition.
(asylum is a kind of shelter)
'unknown number in a favela' is the wordplay.
'unknown number' becomes 'y' (I've seen this in other clues).
'in' indicates putting letters inside.
'favela' becomes 'slum' (both can mean a poor town or neighbourhood).
'a'+'slum'='aslum'
'y' inserted into 'aslum' is 'ASYLUM'.
(Other definitions for asylum that I've seen before include "Refuge or home for mentally ill" , "Shelter for refugees" , "Sanctuary or kind of hospital" , "Protection given to political refugee" , "Haven or hospital for the mentally ill" .)