Di دي

The Coptic Root: While Ⲡ was masculine, the letter Ⲧ (T / Th) was the foundation for anything feminine in Coptic. The word for "this" (pointing to a female object) was Ⲑⲁⲓ or Ⲧⲁⲓ (Thai or Tai).

Just like the masculine sound shifted, the dental Coptic T/Th sound relaxed in the bilingual Egyptian environment, shifting its articulation point slightly to become a voiced D (د). This turned Thai directly into the modern دي.

The Syntax Rule: In Modern Standard Arabic, you must say Hadhihi al-bint (This the girl). But in Masri, we say البنت دي (El-bint di / "The girl this"). This perfectly mirrors the Coptic phrasing ϯⲁⲗⲟⲩ ⲑⲁⲓ (Ti-alou thai / "The girl this"), keeping the demonstrative pointer locked at the very end of the phrase.