يَوْمِ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – يَوْمِ 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 it changes to اليَوْمِ due to: 1) a preposition that precedes it or 2) a possessed noun that precedes it or 3) it’s a noun of dependent declension a) نَعْتٌ / صِفَطٌ adjectives b) التَّوْكِيْدُ emphatic c) المَعْطُوْفٌ conjunction d) البَدَلُ synonym

اليَوْمِ loses it’s definite article, becoming يَوْمِ 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

Grammatical analysis of يَوْمِ
اسْمٌ مَجْرُوْرٌ بِالكَسْرَةِ الزَّاهِرَةِ وَهُوَ مُضَافٌ
مَعْرِفَةٌمُفْرَدٌمُذَكَّرٌمَجْرُوْرٌي و م جَامِدٌمَجَرَّدٌفَعْلٌاسْمٌاِسْمُ الجِنْسِ
DefiniteSingularMasculineGenitiveRootDayRoot letters onlyPatternNounGeneric or common Noun
Surah/Below are the 46 verses in the holy Quran containing the possessed, genitive nounيَوْمِ
Verse
2-4Owner of the day of recompense (requital, judgement, reckoning)مَالِكِ يَوْمِ الدِّيْنِ
4-87
5-14 
5-36 
5-64 
6-12 
7-14 
7-51 
7-167 
9-77 
15-35 
15-36 
15-38 
17-58 
17-62 
21-47 
23-100 
26-189 
28-71 
28-72 
30-56 
32-14 
37-144 
38-16 
38-53 
38-78 
38-79 
38-81 
39-71 
40-27 
40-30 
45-26 
45-34 
46-5 
51-60 
54-19 
62-9 
64-9 
68-39 
70-26 
74-46 
75-1 
77-13 
83-11 
 
83-11 
 
83-11