this is not a Hebrew word
It is. Machmad מחמד means desirable
Yet I will send my servants unto thee to morrow about this time, and they shall search thine house, and the houses of thy servants; and it shall be, that whatsoever is pleasant (machmad) in thine eyes, they shall put it in their hand, and take it away (1 Kings 20:6)
He hath bent his bow like an enemy: he stood with his right hand as an adversary, and slew all that were pleasant (machamaddei) to the eye in the tabernacle of the daughter of Zion: he poured out his fury like fire (Lamentations 2:4)
Our holy and our beautiful house, where our fathers praised thee, is burned up with fire: and all our pleasant things (machamaddeinu) are laid waste (Isaiah 64:11)
The adversary hath spread out his hand upon all her pleasant things (machamaddeiha) : for she hath seen that the heathen entered into her sanctuary, whom thou didst command that they should not enter into thy congregation (Lamentations 1:10)
Because ye have taken my silver and my gold, and have carried into your temples my goodly pleasant things (machamadday) (Joel 3:5)
Also the word of the Lord came to me, saying, “Son of man, behold, I take away from you the** desire (machmad) **of your eyes with one stroke; yet you shall neither mourn nor weep, nor shall your tears run down (Ezekiel 24:15-16)
Speak unto the house of Israel, Thus saith the Lord GOD; Behold, I will profane my sanctuary, the excellency of your strength, the desire (machmad) of your eyes, and that which your soul pitieth; and your sons and your daughters whom ye have left shall fall by the sword (Ezekiel 24:21)
All her people sigh, they seek bread; they have given their pleasant things (machamaddeihem) for meat to relieve the soul: see, O LORD, and consider; for I am become vile (Lamentations 1:11)
Machmad מחמד is its singular. Machamaddim מחמדים is its plural. Plurals are made adding ים -im: ben (son) → banim (sons). Machamaddeinu is plural with the pronoun “nu” (our) at the end. When the pronoun attaches to the plural, "im" changes to "ei": banim (sons) → baneinu (our sons)
"Maḥammadim" is NOT related to the Hebrew word "Mahmad"
If it is its plural then how is it not related? That's like saying "men" is not related to "man"
It is intensive plural to make its meaning stronger, i.e. “very lovely”. We see another example of that in the same verse: chikko mamtaqqim (his mouth is most sweet). Chikko is singular, but mamtaqqim is plural, meaning “very sweet”. Another example of intensive plural:
ואהיה אצלו אמון ואהיה שעשעים יום יום משחקת לפניו בכל עת
Waehyeh etslo amon waehyeh shaashuim yom yom mesacheket lefanav bechol et
Then I was by him, as one brought up with him: and I was daily his delight, rejoicing always before him;
Proverbs 8:30
לא יתנני השב רוחי כי ישבעני ממררים
Lo yitteneni hashev ruchi ki yasbiani mammerorim
He will not allow me to catch my breath, But fills me with bitterness
Job 9:18
Significance of 'ten thousand' (5:10 what does '...chiefest among ten thousand...')?
Majority of translations don't use the word "chiefest", but "better" or "outstanding". The word Rebabah רבבה is often used for a very large number. 10,000 is אשר אלפים
The context implies that it is not a name. The verse says “wechullo machamaddim”. “We” means “and”. “Chull” means “all”, “whole”, “every” and “o” means “of him”, like in “chikko” (his mouth, chik - mouth, o - of him, his). So “wechullo” means “and all of him is”, not "and he is”. All its translations are like this:
His mouth is most sweet: yea, he is altogether lovely. This is my beloved, and this is my friend, O daughters of Jerusalem (King James Version)
His mouth is sweetness, and all of him is desirable. This is my beloved, this is my friend, young women of Jerusalem! (International Standart Version)
His mouth is sweetness itself; he is desirable in every way. Such, O women of Jerusalem, is my lover, my friend (New Living Translation)
His mouth is full of sweetness. And he is wholly desirable. This is my beloved and this is my friend, You daughters of Jerusalem (New American Standart Bible)
His mouth is sweetness itself; he is delightful in every way. Such is my lover, and such my friend, Daughters of Jerusalem! (New American Bible)
His mouth is very sweet; he is totally desirable. This is my beloved! This is my companion, O maidens of Jerusalem! (NET Bible)
His speech is most sweet, and he is altogether desirable. This is my beloved and this is my friend, O daughters of Jerusalem (New Revised Standart Version)
Saying “all of him is Muhammad", "he is altogether Muhammad" isn't that correct. If there is a person who is wholly Muhammad, so there can be also people who are a little bit Muhammad, half Muhammad, mostly Muhammad etc. As a name it doesn't fit into this. “He is altogether lovely" or "all of him is desirable" makes more sense. It means that everything in this person is pleasant, there is nothing unpleasant in him