لَيْلَةُ

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

الَّيْلَةُ is the natural state of this definite noun and it is in this state ( مَرْفُوْعٌ) when the noun is: 1) the subject المُبْتَدَأُ or 2) the predicate الخَبَرُ or 3) اسْمُ كَانَ or 4) خَبَرُ إِنَّ or 5) الفَاعِلُ subject of a verb in the active voice or 6) نَائِبُ الفَاعِلِ subject of a verb in the passive voice or 7) it’s a noun of dependent declension a) نَعْتٌ / صِفَطٌ adjectives b) التَّوْكِيْدُ emphatic c) المَعْطُوْفٌ conjunction d) البَدَلُ synonym

الَّيْلَةُ loses it’s definite article, changing to لَيْلَةُ due to it being a possessed noun

Night

الْمَعْرِفَةُمُفْرَدٌمُؤَنَّثٌمَرْفُوْعٌل ي لبَابٌ فَعْلَةٌاسْمٌالْمَصْدَرُ
DefiniteSingularFeminineNominativeRootNightPatternNounVerbal noun
مَصْدَرُ الْمَرَّةِ
Surah/Below are the 2 verses in the holy Quran containing the nominative, possessed nounلَيْلَةُ
Verse
97-2And what will make you know what the night of Qadr is?وَمَآ أَدْرَاكَ مَا لَيْلَةُ القَدْرِ
97-3The night of Qadr is better than a thousand monthsلَيْلَةُ القَدْرِ خَيْرٌ مِّنْ أَلْفِ شَهْرٍ