He tyrannises the poor working newspapermen in it (9)
I believe the answer is:
oppressor
'he tyrannises' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'poor working newspapermen in it' is the wordplay.
'working' indicates anagramming the letters.
'newspapermen' becomes 'press' (I can't justify this - if you can you should give a lot more credence to this answer).
'in it' indicates putting letters inside.
'poor' is an anagram of 'opor'.
'opor' enclosing 'press' is 'OPPRESSOR'.
'the' is the link.
Can you help me to learn more?
(Other definitions for oppressor that I've seen before include "One who keeps another in subjection" , "Despot" , "Proposers for one who persecutes" , "One subjects others to undue pressure" , "Persecutor of proposers" .)