The most common and most likely answer to this crossword clue is the 4 letter word AMEN
I've seen this crossword clue in Financial Times
A
M
E
N
More clues leading to the result AMEN
- Final word is not quite correct
- Change of name? I'll second that
- Answer people, having the last word
- The last word in glam entertainment
- Congregation's response put right without end
- Response from congregation almost put right
- To ratify in parliament
- The last word in steam engineering
- Primarily: ‘Agreed! Manifestly! Endorsed! Naturally!‘
- Males below average to begin with? So be it
Buddy explains!

The straight part
We know that "The last word" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the last word = amen.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AMEN mean?
AMEN noun- An instance of saying ‘amen’.
- A title of Christ; the Faithful One (especially with reference to Revelation 3:14)
- To say amen.
- To say amen to; to ratify solemnly.
- At the end of religious prayers: so be it.
- In many Abrahamic religious texts and creeds: truly, verily.
- An expression of strong agreement. Often, though dated, in the phrase "Amen to that".