Fifty-four? I would be furious (5)
I believe the answer is:
livid
'furious' is the definition.
(both can mean very angry)
'fifty-four? i would' is the wordplay.
'fifty' becomes 'L' (Roman numeral).
'four?' becomes 'iv' (Roman numerals).
'i would' becomes 'I'd'.
'l'+'iv'+'id'='LIVID'
'be' is the link.
(Other definitions for livid that I've seen before include "Very cross" , "Furious - discoloured from bruise" , "Really angry, the colour of lead" , "Bluish-grey" , "... annoyed" .)