_ora B_? Completing it would be smart (5)
I believe the answer is:
natty
'be smart' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
(Other definitions for natty that I've seen before include "Stylishly dressed" , "Smartly dressed" , "Stylish" , "Smart, spruce" , "Dapper (colloq.)" .)