Joint ought to be livelier, ultimately (8)
I believe the answer is:
shoulder
'joint' is the definition.
(shoulder is a kind of joint)
'ought to be livelier ultimately' is the wordplay.
'ought to' becomes 'should' ('you ought to' means 'you should').
'ultimately' indicates one should take the final letters.
The final letters of 'be livelier' are 'er'.
'should'+'er'='SHOULDER'
(Other definitions for shoulder that I've seen before include "Carry a burden" , "Upper body joint" , "Cut of meat" , "hard on the motorway" , "Bear < to push" .)