Earl received by respectable relative (5)
I believe the answer is:
niece
'relative' is the definition.
(type of relative)
'earl received by respectable' is the wordplay.
'earl' becomes 'e'.
'received by' means one lot of letters goes inside another.
'respectable' becomes 'nice' (similar in meaning).
'e' inserted inside 'nice' is 'NIECE'.
(Other definitions for niece that I've seen before include "A younger female relative" , "Female relation" , "Brother's daughter" , "Young female relative" , "[PRIEST'S] daughter?" .)