First there are the primary meanings of Khatam and then there are the metaphorical meanings of Khatam. The primary meaning of Khatam according to Imam Raghib is that of seal and putting impression on something else. Then we have the metaphorical meanings which are used to mean to stop or close something.
The first meanings are the impression of one thing on another and all of the other meanings are metaphorical meanings.
So the word Khatam is Ism ala from Khatama and Khaatim is ism faa’il. Khatam means the means of putting impression on something and Khaatim is the one that puts the impression. This means that prophet would be greater than all other Prophets.
When these words come with a group, then it means that through whose impression others were born of the same category. This is how Arabs have used this. In the metaphorical way, it was has been used as last as well but when the real meaning can be taken, one does not turn to the metaphorical meaning. Hadrat Ahmad (as) himself used Khatam to mean as last in majaazi sense for Khatamul Aulaad and Khatamul anbiya for Bani Israel using the example of Hadrat Isa (as).
Ahmadas states:
“Thirdly, I am also similar to Adam in that Adam was born as a twin and I was also born as a twin. First a girl was born and I was born thereafter; and in this manner I was Khatamul-Walad for my father. No child was born after me.”(Brahin-e-Ahmadiyya Ruhani Khazain Volume 21. Page 113)
He further states:
“A girl was born with me whose name was Jannat. First she was born and then I was delivered. After me there was no son or daughter born to my parents and I was Khatamul-Aulad for them.”(Taryaqul Qulub, Ruhani Khazain Volume 15, Page 479)
Now none of these references contradict our belief on what khatme nabuwat means to begin with. Khatam can be used as last for us and it will still not affect our belief in any way. We agree that the Promised Messiahas is the last of the children in the same way the Holy Prophetsaw is the last of the prophets.
When Ahmadas states that he is khatamul Aulad and that no child was born after him, it does not refer to last in the way the non Ahmadis take it to be.
Another important factor to be noted is that Ahmadi Muslims do not deny that Khatam can be used for last when not referring to rank. We see this explained in Review of Religions of Religions of 1986 where it is written:
“Khatamul- Aulad (last of sons) will mean last born because to be born is not a talent and the term is used not to praise the boy but merely to point out the fact that he is the youngest son.”
This shows us that such titles can also have the meaning of last, as it is not a talent or a term used to praise someone.
Page 98 onwards explains that Khatam has its primary meanings and then metaphorical meanings for last as well.