One of a bear trio (4)
I believe the answer is:
papa
'one of a bear trio' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for papa that I've seen before include "Daddy]" , "Father; P (radio comms.)" , "Dad" , "Comms code for 'P'" , "Mama's other half?" .)