Roars during day end squabbling (8)

'roars' is the definition.
('thunder' can be a synonym of 'roar')

'during day end squabbling' is the wordplay.
'during' is an insertion indicator.
'day' becomes 'thurs' (short for Thursday).
'end' says to hollow out the word (remove centre letters) (I've seen 'ends' mean this).
'squabbling' becomes 'unde' (I can't justify this - if you can you should believe this answer much more).
'thurs' with its centre removed is 'thrs'.
'thrs' placed around 'unde' is 'THUNDERS'.

Can you help me to learn more?