Work over, turned up with son (4)
I believe the answer is:
opus
'work' is the definition.
(I've seen this before)
'over turned up with son' is the wordplay.
'over turned' becomes 'upo' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'with' says to put letters next to each other.
'son' becomes 's'.
'upo' backwards is 'opu'.
'opu'+'s'='OPUS'
Can you help me to learn more?
(Other definitions for opus that I've seen before include "Creative work, eg in writing, art or music" , "Piece of music (with number)" , "Soup (anag.)" , "Work of 25 perhaps" , "A Latin work" .)