510 β number of the beast? (4)
I believe the answer is:
lion
'the beast?' is the definition.
(type of animal)
'510 number of' is the wordplay.
I cannot quite see how this works, but
'number' could be 'l' (L is an example) and 'l' is found in the answer.
'of' could be 'o' and 'o' is present in the answer.
The remaining letters 'in' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for lion that I've seen before include "Buddhist scripture; Sanskrit rule" , "Important figure" , "British RU cap" , "King of the jungle" , "Sought after celebrity (showing great strength and courage?)" .)