Polite to welcome English relative (5)
I believe the answer is:
niece
'relative' is the definition.
(I know that relative can be written as niece)
'polite to welcome english' is the wordplay.
'polite' becomes 'nice' (I've seen this in another clue).
'to welcome' indicates putting letters inside (in sense of 'inviting in').
'english' becomes 'e' (abbreviation).
'nice' placed around 'e' is 'NIECE'.
(Other definitions for niece that I've seen before include "girl further down the line" , "Criminal" , "member of different generation" , "Family relative" , "One of the family" .)