Ring little brother up (3)
I believe the answer is:
orb
'ring' is the definition.
(I've seen this before)
'little brother up' is the wordplay.
'little brother' becomes 'bro'.
'up' is a reversal indicator (in down clue: letters go upwards).
'bro' reversed gives 'ORB'.
(Other definitions for orb that I've seen before include "The World" , "Ornamental sphere" , "Part of royal regalia" , "Ceremonial globe carried by a monarch" , "A poetic eye, bro" .)