About fifty underneath roar like bulls (6)

I believe the answer is:

bellow

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'roar like bulls' is the definition.
'bellow' can be an answer for 'roar' (synonyms). I am not sure about the 'like bulls' bit.

'about fifty underneath' is the wordplay.
'about' means one lot of letters goes inside another.
'fifty' becomes 'l' (Roman numeral).
'underneath' becomes 'below' (I've seen this before).
'l' going within 'below' is 'BELLOW'.

Can you help me to learn more?

(Other definitions for bellow that I've seen before include "author" , "Deep roar as of bull" , "Loud cry of a bull" , "Loud and deep roar" , "Roar like a bull" .)

I've seen this clue in The Irish Independent.

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