القَمَرِ

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

القَمَرُ is the natural state of this definite noun and it changes to القَمَرِ 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

Moon

To be white

مَعْرِفَةٌمُفْرَدٌمُذَكَّرٌمَجْرُوْرٌق م ربَاب ضَرَبَفَعَلٌقَلَمَ يَقْلِمُاسْمٌاِسْمُ الجِنْسِ
DefiniteSingularMasculineGenitiveRootMoonPatternض / نNounGeneric or common Noun
Surah/Below are the 4 verses in the holy Quran containing the genitive, definite nounالقَمَرِ
Verse 
and among His signs are the night and the day and the sun and the moonوَمِنْ ءَايَاتِهِ الَّيْلُ وَالنَّهَارُ وَالشَّمْسُ وَالقَمَرُ
do not prostrate to the sun and not to the moon but prostrate to Allah (SWT) who created themلَا تَسْجُدُوا لِلشَّمْسِ وَلَا لِلقَمَرِ وَاسْجُدُوا لِلَّهِ الَّذِى خَلَقَهُنَّ
41-37if it is Him you worshipإِنْ كُنْتُمْ إِيَّاهُ تَعْبُدُوْنَ
74-32nay! by the moonكَلَّا وَالقَمَرِ
84-18and by the moon when it becomes fullوَالقَمَرِ إِذَا اتَّسَقَ
91-2and the moon when it follows it (the sun)وَالقَمَرِ إِذَا تَلَاهَا