Animated officer half-heartedly supporting member of staff getting part in The Bill (8)

I believe the answer is:
mandible
'animated officer' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'half-heartedly supporting member of staff getting part in the bill' is the wordplay.
'half-heartedly' becomes 'dle' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'member of staff' becomes 'man' (man can mean a worker or member of a staff).
'getting' indicates putting letters inside.
'part' suggests taking the first letters.
The initial letters of 'in bill' is 'ib'.
'dle' put after 'man' is 'mandle'.
'mandle' going around 'ib' is 'MANDIBLE'.
Can you help me to learn more?
(Other definitions for mandible that I've seen before include "Mammal lower jawbone" , "Ambled in bearing lower jaw" .)
