Joke always largely upset square (6)

'square' is the definition.
I know nothing about this answer so I can't tell whether this works.

'joke always largely upset' is the wordplay.
'joke' becomes 'pun' (pun is a type of joke).
'always' becomes 'ever' (synonyms).
'largely' means to remove the last letter (most but not all of the letters).
'upset' shows that the letters should be reversed in order.
'pun'+'ever'='punever'
'punever' with its last letter removed is 'puneve'.
'puneve' in reverse letter order is 'EVENUP'.

Can you help me to learn more?