Roughage at last eaten by pleasant relative (5)
I believe the answer is:
niece
'relative' is the definition.
(type of relative)
'roughage at last eaten by pleasant' is the wordplay.
'at last' suggests the final letters.
'eaten by' is an insertion indicator (inserted letters get eaten).
'pleasant' becomes 'nice' (similar in meaning).
The final letter of 'roughage' is 'e'.
'e' placed inside 'nice' is 'NIECE'.
(Other definitions for niece that I've seen before include "Daughter of a sibling" , "girl further down the line" , "Brother's girl" , "Brother or sister's daughter" , "Brother's daughter" .)