Realise that work must be finished immediately (4)
I believe the answer is:
know
'realise that work' is the definition.
'know' can be an answer for 'realise' (I've seen this before). I am unsure of the rest of the definition.
'finished immediately' is the wordplay.
'finished' becomes 'k' (I can't justify this - if you can you should believe this answer much more).
'immediately' becomes 'now' (I've seen this in another clue).
'k'+'now'='KNOW'
'must be' is the link.
Can you help me to learn more?
(Other definitions for know that I've seen before include "Recognise" , "Understand" , "Have information" , "Have awareness of" , "Be acquainted with" .)