Old bloke extremely negligent about a new contract (8)
I believe the answer is:
covenant
'contract' is the definition.
(covenanting is a kind of contracting)
'old bloke extremely negligent about a new' is the wordplay.
'old bloke' becomes 'cove' (cove is an old-fashioned term for a man).
'extremely' suggests removing the centre (only the extremes of the word are used).
'about' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'negligent' with its middle removed is 'nt'.
'a'+'n'='an'
'nt' going around 'an' is 'nant'.
'cove'+'nant'='COVENANT'
(Other definitions for covenant that I've seen before include "Legal agreement" , "Signed agreement between two or more to do something" , "Formal agreement between two or more parties" , "Contract made in a convent" , "Concordat, compact" .)