I object again to the Maori war club (4)
I believe the answer is:
mere
'the maori war club' is the definition.
(I've seen this in another clue)
'i object again' is the wordplay.
'i object' becomes 'me'.
'again' becomes 're' (prefix meaning 'again').
'me'+'re'='MERE'
'to' acts as a link.
(Other definitions for mere that I've seen before include "Insignificant" , "DDwater" , "Former lake" , "Nothing more than - water" , "Without additions or modifications" .)