Upstart in final part about bear (6)
I believe the answer is:
endure
'bear' is the definition.
(both can mean to tolerate)
'upstart in final part about' is the wordplay.
'upstart' becomes 'u' (start of the word 'up').
'in' is an insertion indicator.
'final part' becomes 'end' (I've seen this before).
'about' becomes 're' (regarding).
'end'+'re'='endre'
'u' placed into 'endre' is 'ENDURE'.
(Other definitions for endure that I've seen before include "Abide" , "Last or tolerate" , "Tolerate, put up with" , "Persist over time" , "Undergo a tough time" .)