Half of drawing revealed secret bones (8)
I believe the answer is:
skeleton
'bones' is the definition.
(I've seen this before)
'half of drawing revealed secret' is the wordplay.
'half of' indicates taking half.
'drawing' becomes 'sketch' (sketch is a kind of drawing).
'revealed secret' becomes 'leton' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sketch' cut in half is 'ske'.
'ske'+'leton'='SKELETON'
Can you help me to learn more?
(Other definitions for skeleton that I've seen before include "Body frame" , "Bodily frame" , "Frame - secret scandal" , "Bone structure" , "emaciated type" .)