حِجْرٍ

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

حِجْرٌ is the natural state of this indefinite noun and it becomes حِجْرٍ 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

Anything forbidden, unlawful; Wall or dam; Intelligence; Understanding

To deprive from, harden, hide, resist, forbid, prevent, hinder, prohibit access (to a place)

Surah/Below is the 1 verse in the holy Quran, containing the indefinite, genitive nounحِجْرٍ
Verse 
89-5Are there (not) in these (oaths) a proof for men of understanding?هَلْ فِي ذَلِكَ قَسَمٌ لِذِي حِجْرٍ