مَالِكِ

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

المَالِكُ is the natural state of this definite noun and changes to المَالِكِ 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

المَالِكِ loses it’s definite article, becoming مَالِكِ due to it being a possessed noun

Lord, Master, Owner, Sovereign, Who possesses the right over a thing and has the power to deal with it as one likes

Grammatical analysis of مَالِكِ
اسْمٌ مَجْرُوْرٌ بِالكَسْرَةِ الزَّاهِرَةِ وَهُوَ مُضَافٌ
مَعْرِفَةٌمُفْرَدٌمُذَكَّرٌمَجْرُوْرٌم ل كبَاب ضَرَبَمَلَكَ يَمْلِكُفَاعِلٌاسْمٌاِسْمُ الْفَاعِلُ
DefiniteSingularMasculineGenitiveRootOwnerضPatternNounActive participle
     Lord    
     Master    
     Sovereign    
     Possesses the right    
Surah/Below is the only verse in the holy Quran containing the genitive, possessed nounمَالِكِ
Verse
1-4Owner/Master of the day of recompense/requital/judgement/reckoningمَالِكِ يَوْمِ الدِّيْنِ