A fifty pound total (3)
I believe the answer is:
all
'total' is the definition.
(I've seen this in another clue)
'a fifty pound' is the wordplay.
'fifty' becomes 'l' (Roman numeral).
'pound' becomes 'l' (abbreviation e.g. Lsd - pounds, shillings, pence).
'a'+'l'+'l'='ALL'
(Other definitions for all that I've seen before include "'Bless 'em - - ' (song)" , "Everybody; everything" , "Avenue, walk or garden path" , "Monopolist controls this" , "Every single one" .)