خَوْفٌ

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

خَوْفٌ is the natural state of this indefinite noun and it is in this state ( مَرْفُوْعٌ) when the noun is: 1) المُبْتَدَأُ or 2) 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