العُسْرِ

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

العُسْرُ is the natural state of this definite noun and it became الْعُسْرِ 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

Hardship

To be difficult, hard

Surah/Below are the 2 verses in the holy Quran, containing the genitive nounالعُسْرِ
Verse
94-5Surely, along with hardship is reliefفَإِنَّ مَعَ الْعُسْرِ يُسْرًا
94-6Surely, along with hardship is reliefإِنَّ مَعَ الْعُسْرِ يُسْرًا