يَوْمَ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – يَوْمَ is a noun

A noun may either be 1) Definite or indefinite 2) Masculine or feminine 3) Singular, dual or plural 4) Nominative, accusative or genitive

اليَوْمُ is the natural state of this definite noun and becomes اليَوْمَ due to it being the: 1) المَفْعُوْلُ بِهِ object of a verb or 2) اسْمُ of إِنَّ or 3) خَبَرُ of كَانَ or 4) المَفْعُوْلُ فِيْهِ adverb of time or place or 5) المَفْعُوْلُ لَهُ noun that gives the reason for doing a thing or 6) المَفْعُوْلُ مَعَهُ noun that comes after the و which means “along with” or 7) المَفْعُوْلُ المُطْلَقُ is the مَصْدَرٌ of the verb occurring in the sentence or 8) الحَالُ adverb of manner or 9) التَّمْيِيْزُ noun that specifies the meaning of a vague word or 10) المُسْتَثْنَى noun that comes after إِلَّا meaning “except” or 11) المُنَادَى noun of calling or 12) it’s a noun of dependent declension a) نَعْتٌ / صِفَطٌ adjectives b) التَّوْكِيْدُ emphatic c) المَعْطُوْفٌ conjunction d) البَدَلُ synonym

اليَوْمَ loses it’s definite article, becoming يَوْمَ due to it being a possessed noun

Day, time, day of a battle, thousand years (22-47), fifty thousand years (70-4), Aeon, Day and night, moment

To be one, exist for a day, spend, last a day

Surah/Below are the 54 verses in the holy Quran containing the possessed, accusative noun/adverb of timeيَوْمَ
Verse
Then you are those who kill one anotherثُمَّ أَنْتُمْ هَاؤُلَآءِ تَقْتُلُوْنَ أَنْفُسَكُمْ
and you expel a party of you from their homesوَتُخْرِجُوْنَ فَرِيْقًا مِّنْكُمْ مِّنْ دِيَارِهِمْ
cooperating against them in sin and oppressionتَظَاهَرُوْنَ عَلَيْهِمْ بِالإِثْمِ وَالعُدْوَانِ
and if they come to you as captives, you ransom themوَإِنْ يَأْتُوْكُمْ أُسَارَى تُفَادُوْهُمْ
although their eviction was forbidden to youوَهُوَ مُحَرَّمٌ عَلَيْكُمْ إِخْرَاجُهُمْ
Do you believe in part of the book and disbelieve in part?أَفَتُؤْمِنُوْنَ بِبَعْضِ الكِتَابِ وَتَكْفُرُوْنَ بِبَعْضٍ
So, what is the recompense for them who do that among youفَمَا جَزَآءُ مَنْ يَفْعَلُ ذَلِكَ مِنْكُمْ
except disgrace in the life of this worldإِلَّا خِزْيٌ فِيْ الحَيَاةِ الدُّنْيَا
and on the day of resurrection, they will be subjected to the harshest punishmentوَيَوْمَ القِيَامَةِ يُرَدُّوْنَ إِلَى أَشَدِّ العَذَابِ
2-85and Allah (SWT) is not unaware of what you doوَمَا اللهُ بِغَافِلٍ عَمَّا تَعْمَلُوْنَ
2-113 
2-174 
2-212 
3-30 
3-77 
3-106 
3-155 
3-166 
3-180 
3-185 
3-194 
4-109 
4-141 
4-159 
5-109 
6-22 
6-73 
6-128 
6-141 
6-158 
7-32 
7-53 
7-163 
7-172 
8-41 
19-15 
19-33 
19-38 
19-39 
19-95 
20-100 
20-101 
20-124 
24-24 
41-19 
50-44 
54-6 
60-3 
64-9 
66-8 
68-42 
70-8 
73-14 
the day the spirit and the angels will stand in rows, they will not speakيَوْمَ يَقُوْمُ الرُّوْحُ وَالمَلَآئِكَةُ صَفًّا لَّا يَتَكَلَّمُوْنَ
78-38except whom the Most-Merciful permits him and he will say what is correctإِلَّا مَنْ أَذِنَ لَهُ الرَّحْمَانُ وَقَالَ صَوَابًا
Indeed, We warn you of a near punishmentإِنَّآ أَنْذَرْنَاكُمْ عَذَابًا قَرِيْبًا
the day when man will see what his hands have sent forthيَوْمَ يَنْظُرُ المَرْءُ مَا قَدَّمَتْ يَدَاهُ
78-40and the disbeliever will say, “woe to me! would that I be dust”وَيَقُوْلُ الكَافِرُ يَا لَيْتَنِي كُنْتُ تُرَابًا
79-6the day the one who quakes, quakesيَوْمَ تَرْجُفُ الرَّاجِفَةُ
79-35the day man will remember what he strove forيَوْمَ يَتَذَكَّرُ الإِنْسَانُ مَا سَعَى
On the day they see it, it will feel as if theyكَأَنَّهُمْ يَوْمَ يَرَوْنَهَا
79-46not they remained except an evening or a morningلَمْ يَلْبَثُوآ إِلَّا عَشِيَّةً أَوْ ضُحَاهَا
80-34the day when man will flee from his brotherيَوْمَ يَفِرُّ المَرْءُ مِنْ أَخِيْهِ
82-15They will burn in it on the day of judgementيَصْلَوْنَهَا يَوْمَ الدِّيْنِ
83-6a day man will stand before the Lord of Creationيَوْمَ يَقُوْمُ النَّاسُ لِرَبِّ العَالَمِيْنَ
86-9The day secrets will be put on trialيَوْمَ تُبْلَى السَّرَآئِرُ
101-4it is a day when the people will be like scattered mothيَوْمَ يَكُوْنُ النَّاسُ كَالْفَرَاشِ الْمَبْثُوْثِ