Burden a person usually conceals (4)
I believe the answer is:
onus
'burden' is the definition.
('onus' can be a synonym of 'burden')
'a person usually conceals' is the wordplay.
'conceals' says the answer is hidden in the clue.
'ONUS' is hidden within 'a person usually'.
(Other definitions for onus that I've seen before include "'Burden, load (4)'" , "albatross?" , "Duty or responsibility" , "Responsibilty" , "Liability" .)