Relation's arrival welcomed by mother (9)
I believe the answer is:
narrative
'relation's' is the definition.
(a narrative is related or told)
'arrival welcomed by mother' is the wordplay.
'arrival' becomes 'arr' (abbreviation used in transport).
'welcomed by' indicates putting letters inside (letters welcomed inside).
'mother' becomes 'native' (as in a native or mother tongue).
'arr' placed within 'native' is 'NARRATIVE'.
(Other definitions for narrative that I've seen before include "Popeye's vegetable" , "Story line" , "Storyline" , "Story recounting events" , "Chronicle" .)