Half Greeks back showing some work (3)
I believe the answer is:
erg
'some work' is the definition.
(an erg is a unit of work done)
'half greeks back' is the wordplay.
'half' suggests halving the letters.
'back' is a reversal indicator.
'greeks' halved is 'gre'.
'gre' backwards is 'ERG'.
'showing' is the link.
(Other definitions for erg that I've seen before include "Energy expended" , "shifting sand" , "What's used to record work" , "Unit of work (phys.)" , "Unit of work; dunes area" .)