Let out by a tenant (8)
I believe the answer is:
resident
'a tenant' is the definition.
(thesaurus)
'let out by' is the wordplay.
'let' becomes 'rent' (synonyms).
'out' indicates putting letters inside.
'by' becomes 'side' (synonyms).
'rent' going around 'side' is 'RESIDENT'.
(Other definitions for resident that I've seen before include "one in the house?" , "Lodger" , "Occupant's" , "Inmate" , "One living in the place referred to" .)