Give up work again: get fed up with it (6)
I believe the answer is:
retire
'give up work' is the definition.
(I've seen this before)
'again get fed up with it' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'get fed up' becomes 'tire' (I can't justify this - if you can you should believe this answer much more).
'with it' says to put letters next to each other.
're'+'tire'='RETIRE'
Can you help me to learn more?
(Other definitions for retire that I've seen before include "Give up working and go to bed" , "Quit work, take pension" , "Pull back" , "call it a day" , "Get your head down" .)