ضُحَا

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

الضُّحَى is the natural state of this definite noun and it remains الضُّحَى even though it is in the genitive case 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

because the third radical in الضُّحَى is a weak letter (و or ي) and weak letters do not show their endings, their endings have to be estimated (deduced by reason)

الضُّحَى loses it’s definite article ال, changing to ضُحَا due to it being a possessed noun

Morning, brightness

To be smitten by sunbeams, suffer from the heat of the sun, become uncovered, be revealed, appear conspicuously

مَعْرِفَةٌمُفْرَدٌمُذَكَّرٌمَجْرُوْرٌض ح وبَاب فَتَحَضَحَى يَضْحَىفُعَلٌاسْمٌالْاِسْمُ الجِنْسُ
DefiniteSingularMasculineGenitiveRootBrightnessفPatternNounGeneric / common noun
Surah/Below are the 3 verses in the holy Quran containing the genitive nounضُحَا
Verse
79-29and He darkened its night and brought out its brightnessوَأَغْطَشَ لَيْلَهَا وَأَخْرَجَ ضُحَاهَا
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
91-1By the sun and its brightnessوَالشَّمْسِ وَضُحَاهَا