Persistence of number taking a large town (8)
I believe the answer is:
tenacity
'persistence' is the definition.
('tenacity' can be a synonym of 'persistence')
'number taking a large town' is the wordplay.
'number' becomes 'ten' (ten is a kind of number**).
'taking' is a charade indicator (letters next to each other).
'large town' becomes 'city' (I've seen this before).
'ten'+'a'+'city'='TENACITY'
'of' is the link.
(Other definitions for tenacity that I've seen before include "Doggedly pursuing" , "Firmness of hold" , "Persistence in holding on" , "Perseverance in chosen course" , "Stubbornness, determination" .)