Bear has an obligation to the Queen (8)
I believe the answer is:
shoulder
'bear' is the definition.
(both can mean to carry or take responsibility for)
'has an obligation to the queen' is the wordplay.
'has an obligation to' becomes 'should' (I've seen this in another clue).
'the queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'should'+'er'='SHOULDER'
(Other definitions for shoulder that I've seen before include "Joint between the neck and arm" , "hard on the motorway" , "Undertake (burden)" , "Top of the arm" , "Joint - ours held (anag)" .)