Mean to alter the last word (4)
I believe the answer is:
amen
'last word' is the definition.
(last word in a prayer)
'mean to alter' is the wordplay.
'to alter' indicates an anagram.
'mean' with letters rearranged gives 'AMEN'.
'the' is the link.
(Other definitions for amen that I've seen before include "Conclusion of prayer" , "Word of approval" , "Extremist" , "Name for end to prayer" , "Final word in prayer" .)