As a result, work unit introduces nothing (4)
I believe the answer is:
ergo
'as a result' is the definition.
(therefore)
'work unit introduces nothing' is the wordplay.
'work unit' becomes 'erg' (erg is a kind of work unit).
'introduces' is a charade indicator (letters next to each other) (some letters come before or introduce others).
'nothing' becomes 'O' (O resembles 0).
'erg'+'o'='ERGO'
(Other definitions for ergo that I've seen before include "'Therefore, to the old Romans (4)'" , "Hence" , "'Cogito, ---- sum'" , "for this reason" , "so philosopher wrote in Latin" .)