Party may finish off in field (6)
I believe the answer is:
domain
'field' is the definition.
(I know that field can be written as domain)
'party may finish off in' is the wordplay.
'party' becomes 'do' (do can informally mean a party).
'finish off' means to remove the last letter.
'may' with its last letter taken away is 'ma'.
'do'+'ma'+'in'='DOMAIN'
(Other definitions for domain that I've seen before include "Realm or range of influence" , "Territory over which someone reigns" , "Kingdom or realm" , "Scope of knowledge - owned land" , "Territory over which rule or control is exercised" .)