Exceedingly angry quartet breaking cover (5)

I believe the answer is:

livid

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'exceedingly angry' is the definition.
'livid' can be an answer for 'angry' (I've seen this in another clue). I'm not certain of the 'exceedingly' bit.

'quartet breaking cover' is the wordplay.
'quartet' becomes 'IV' (Roman numerals for four).
'breaking' indicates putting letters inside.
'cover' becomes 'lid' (lid is a kind of cover).
'iv' put into 'lid' is 'LIVID'.

Can you help me to learn more?

(Other definitions for livid that I've seen before include "Furious (informal)" , "Enraged" , "Black and blue" , "Bloodless" , "infuriated" .)

I've seen this clue in The Globe and Mail.

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