الوَادِ

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

الوَادُ is the natural state of this definite noun and it becomes الوَادِ 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

Valley

To pay the blood money, pay a fine as expiation for human life, compensate for murder

Surah/Below are the 4 verses in the holy Quran containing the nounالوَادِ
Verse 
20-12
28-30
79-16when his Lord called him in the sacred valley of Tuwaإِذْ نَادَاهُ رَبُّهُ بِالوَادِ المُقَدَّسِ طُوًى
89-9and Thamud who hewed out rocks in the valleyوَثَمُوْدَ الَّذِيْنَ جَابُوْا الصَّخْرَ بِالْوَادِ