The Ahmadis compiled their own dictionary of the words of the Qur’an titled Dictionary of the Holy Qur’an. Written by Malik Ghulam Farid, under the Publisher’s Note (page 5 on the pdf), it claims to be entirely based off of Lisan al-’Arab, Taaj al-’Aroos, al-Mufridaat fi Ghareeb al-Qur’an, Arabic-English Lexicon by E.W. Lane and Aqrab al-Mawarid.

On pages 222-223, regarding the word خاتم, Farid wrote:

خاتَمٌ also means the best and most perfect; embellishment or ornament; the hollow of the back of the neck: وَلَكِن رَّسُولَ اللَّهِ وَخَاتَمَ النَّبِيِّينَ But he is the Messenger of Allah and the seal of the Prophets (33:41)

I openly challenge the validity of this entry by Farid.  خاتم has many meanings, but ‘best’, ”most perfect’,’ embellishment’ or ‘ornament’ are not amongst them, nor can they be directly implied by any classical lexicon Farid referenced.  All of the referenced lexicons say خاتم means ‘last’ in some form or another, and some specifically give the example of Surah Ahzab verse 40 (41) as listed above to mean Last of the Prophets.  Below are the original Arabic texts and English translations of these dictionaries/lexicons.  Notice that none of them, without exception, say خاتم means ‘best’, ‘most perfect’, ‘embellishment’ or ‘ornament’.

Lisaan al-‘Arab لسان العرب

(خَتَمَ)
وخَتَمَ الشيءَ خَتْمًا بلغ آخرهُ
والقرآن والكتاب قرأَهُ كلَّهُ وأَتَّمَّهُ
والصكَّ وغيرهُ وضع عليهِ نقش خاتمهِ حتى لا يجري عليهِ التزوير والتبديل
وخَتَم العمل فرغ منهُ
والإِنَاءَ سدَّهُ بالطين ونحوهِ
ومنهُ في سورة المطفّفين يُسْقَوْنَ مِنْ رَحِيقٍ مَخْتُومٍ خِتَامُهُ مِسْكٌ وَفِي ذَلِك فَلْيَتَنَافَسِ المُتَنَافَسُون 
الخاتِم والخاتَم الخاتام وآخِر القوم ج خواتم
الخاتمة مؤَنَّث الخاتم. ومن كل شيءِ أقصاهُ وتمامهُ وعاقبتهُ وآخرتهُ كخاتمة الكتاب وغيرهِ وهي نقيض الفاتحة

(Khatama)
Khatama [v.] Khatman [n.] something: reached its ending
the Qur’än and a book: read all of it and comleted it.
a document, or others: put on it a pattern of his seal so it would not be forged or edited
Khatama a job: finished it
a container: sealed it with mud, or so forth.
Also in Sürat AlMuṭaffifïn Qur’än [83:25] 
Khätim, Khätam, Khätäm, and the last of a group, pl. Khawätïm
Khätimah, fem. of Khätim
Of anything: it’s farthest limit, its completion, its end, and outcome
Such as a Khätimah of a book or so forth
and it is the opposite of Fätiħah (opening/opener)

Taaj al-‘Aroos تاج العروس

الخاتم 
من كل شيء عاقبته وآخرته كخاتمته 
و الخاتم : آخر القوم كالخاتم
ومنه قوله تعالى وخاتم النبيين أي آخرهم 
وقد قرئ بضم التاء وقول العجاج
مبارك للأنبياء خاتم

The Khätam
of any thing is its conclusion and its end as Khätimatihi [its closing]
and the Khätam is the last of a group
and of it is the saying of [Allāh] ta`älä “wa-khätama n-nabiyyïn” [and the Seal of Prophets], meaning their last
It was also recited as khatum with a damma on the ta’; and [the poet] al-’Ajjaj said
A blessing to the prophets, this khatam is!

Al-Mufridaat fee Ghareeb al-Qur’an المفردات لغريب القرآن

وخاتم النبيين: الأحزاب/40، لأنه ختم النبوة، أي: تممها بمجيئه

“and the Seal of the Prophets” [Quran Ahzab:40], because he is the seal of prophet hood, that is: he completed it with his coming.

Arabic-English Lexicon by E.W Lane

† The last of a company of men; (Lb, TA ; ) as also ختَمُ and ختِمُ: (K:) whence خَاتَمَ النَّبِيِّينَ † [The last of the prophets], in the Kur [xxxiii. 40]; accord. to one reading, خاتُم, with damm to the ت; (TA;) or الأَنبياء خاتِمُ, i.e. Mohammad; (S;) also called الخاتَمُ and الخاتِمُ.

Aqrab al-Mawarid أقرب الموارد

خَتَمَ: صاحبهُ تَخْتِيمًا: البيهُ الخاتم في اصبعهِ: الاساس
خِتام كل شربٍ: آخرهُ: التاج
خِتام الوادي: افصا هُ و خِتام القوم آخرهم: التاج
زُفَّت اليهِ بخاتم ربّها و ختمها و خِتامها ايوهي في بكارتها: الاساس و التاج بلا تفسير
الخَتْم: بالفتح: لغة في الخاتم ج خُتُوم: التاج
اعطاني خَتْمِي: اي حسي لان حسب الرجل آخر طلبهِ: التاج

“Khattama”: to wear the ring on one’s finger (or place it on someone else’s finger)
“Khitaam” of a drink is its last drop
“Khitaam” of a valley is its endpoint (end of the valley) “Khitaam” of a people (qawm) is their last member
“she was delivered in a wedding procession with her “khaatim” or “khitaam” – (meaning with her virginity intact)
“al-Khatm” is another word (with same meaning) for Khaatim, and the plural of that is khutoom
“he gave me my Khatm”: means my fill/sufficiency, in other words, the last of his desire.”

The following dictionaries were not referenced by Farid.  But, I am providing them only to show that indeed, all classical lexicons completely reject with the Ahmadi invention of the meaning of ‘best’, ‘most perfect’, ‘embellishment’ or ‘ornament’.

Al-Muħït المحيط

Muħït Al-Muħït محيط المحيط

خَتَمَهُ 
ومحمد صلي الله عليه و سلم, خاتِمُ الأَنبياء , عليه وعليهم الصلاة والسلام
التهذيب : والخاتِم والخاتَم من أَسماء النبي
وفي التنزيل العزيز
مَا كَانَ مُحَمَّدٌ أَبَا أَحَدٍ مِنْ رِجَالِكُمْ وَلَكِنْ رَسُولَ اللَّهِ وَخَاتَمَ النَّبِيِّينَ
أَي آخرهم
قال : وقد قرئ وخاتَمَ
وقول العَجَّاج
مُبارَكٍ للأَنبياء خاتِمِ
إِنما حمله على القراءة المشهورة فكسر
ومن أَسمائه العاقب أَيضاً ومعناه آخر الأَنبياء

Khatamahu
and Muħammad PBUH, is the seal of prophets upon him and them be peace and blessing.
Out of respect: AlKhätim and AlKhätam are among the names of the prophet PBUH
and in the Glorious Revelation: Qur’än [33:40]
meaning their last
he says: and it was also read “wa-Khätam”;
and the saying of Al-Àjjäj:
“A blessing to the prophets, this khatam is!”
for he based it on the famous pronunciation [Qirä'ah], so he (ended it with or used) a Kasrah
and among his names is AlÀäqib also, and its meaning is the last of the prophets.

Al-Ghani الغني

خاتِم، خاتَم 
وَلَكِنْ رَسُولُ الله وَخَاتِمُ النَّبِيِّين 
قرآن) آخِرُ الأنْبِيَاءِ
خَتَمَ
خَتَمَ عَمَلَهُ : أنْهَاهُ
خَتَمَ الْكِتابَ : أكْمَلَ قِرَاءتَهُ، أتَمَّه
خَتَمَ الصَّبِيُّ الْقُرْآنَ الْكَرِيمَ : أكْمَلَ حِفْظَهُ وَقِرَاءتَهُ
خَتَمَ لَهُ اللهُ بِالْخَيرِ : جَعَلَ نِهَايَتَهُ سَعِيدَةً

(Khätim, Khätam)
Qur’än [33:40] 
(Qur’än): the last of the prophets
(Khatama)
Khatama his work: Ended it
Khatama the book: completed reading it, completed it
The lad khatama the Noble Qur’än: Completed memorizing and reading it.
Allāh khatama for him with goodness: made his ending happy.

AlWasït الوسيط

الخاتِمُ الخاتامُ… و- من كل شيء: آخره
وفي التنزيل العزيز :مَا كَانَ مُحَمَّدٌ أَبَا أَحَدٍ مِنْ رِجَالِكُمْ وَلَكِنْ رَسُولَ اللَّهِ وَخَاتَمَ النَّبِيِّينَ
الخاتِمةُ: من كل شيء: عاقِبتهُ وآخره

(Khätam): Khätäm… and – of anything: it’s end.
And in the Glorious Revelation: Qur’än [33:40]
(Khätimah): of anything: its end, and last

AlQämüs AlMuħït القاموس المحيط

خَتَمَهُ
كالخاتِم والخاتامِ والخَيْتامِ والخِيتام والخَتَمِ: محرَّكةً (والخاتِيامِ) ج [ج] خَواتِمُ وخَواتِيمُ
وقَد (تَخَتمَ) به ومن كلٌ شيءٍ عاقِبَتُه وآخِرَتُهُ (كخَاتِمتِه) وآخِرُ القَوْمِ

Khatamahu 
(as Khätim, Khätäm, Khaytäm, Khïtam, Khatami) voweled (Khätyäm) [pl.] Khawätïm, Khawätim
Has (Takhattama) with it -
And of anything, its outcome and its ending as. (Khätimatihi), and the last of a group

As you can see, not a single one of the lexicons Farid referenced provide the alternative definition the Ahmadis insist on.  This begs the question, where did he get this definition from?  Did he just make it up?

My initial thought is that he fabricated this entry so that in the future, when Ahmadis reference his work to double-check Surah Ahzab verse 40 (41), they conclude that this verse has nothing to do with the Finality of Prophethood.

In reality, All of the classical interpretators of the Qur’an have concluded that Khaatam an-Nabieen means Last of the Prophets, there are no prophets after Muhammad صلى الله عليه و سلم.

If you wish to double-check my work, most are available here: http://lexicons.sakhr.com/idrisidic_1.asp?Sub=%ce%ca%e3
Here is a scanned copy of Aqrab al-Mawarid made:  http://profile.imageshack.us/user/farhan00/images/detail/#175/aqrabredoht4.jpg
Here is Lane’s Lexicon, page 339: http://www.studyquran.org/LaneLexicon/Volume2/00000339.pdf

May Allah guide the Ahmadis to Islam.