الْفَرَاشِ

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

الْفَرَاشُ is the natural state of this definite noun and it changes to الْفَرَاشِ 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

Moth

To spread out, extend, stretch forth, furnish

Surah/Below is the only verse in the holy Quran containing the definite, genitive nounالْفَرَاشِ
Verse
101-4it is a day when the people will be like scattered mothيَوْمَ يَكُوْنُ النَّاسُ كَالْفَرَاشِ الْمَبْثُوْثِ