Some work is therefore cut short (3)
I believe the answer is:
erg
'some work' is the definition.
(an erg is a unit of work done)
'therefore cut short' is the wordplay.
'therefore' becomes 'ergo' (I've seen this before).
'cut short' means to remove the last letter.
'ergo' with its last letter taken off is 'ERG'.
'is' is the link.
(Other definitions for erg that I've seen before include "Energy expended" , "Unit of work; dunes area" , "Amount of work" , "Shifting dunes in Sahara" , "Unit of measurement of work" .)