Thorny shrub, one accommodated by Remus’s brother (5)
I believe the answer is:
brier
'thorny shrub' is the definition.
'one accommodated by remus's brother' is the wordplay.
'one' becomes 'i' (Roman numeral).
'accommodated by' is an insertion indicator.
'remus's brother' becomes 'brer' (the Uncle Remus stories feature Br'er Rabbit etc).
'i' placed inside 'brer' is 'BRIER'.
(Other definitions for brier that I've seen before include "Thorny bush like the wild rose" , "smoking pipe" , "plant" , "It may be smoked" , "Prickly shrub" .)