Writer returned - he worried first relative (6)
I believe the answer is:
nephew
'relative' is the definition.
(type of relative)
'writer returned he worried first' is the wordplay.
'writer' becomes 'pen' (something which writes).
'returned' says the letters should be written in reverse.
'worried first' becomes 'w' (1st letter of 'worried').
'pen' backwards is 'nep'.
'nep'+'he'+'w'='NEPHEW'
(Other definitions for nephew that I've seen before include "Sister's son" , "Male relative" , "A sibling's child" , "A young male relation" , "Family relative" .)