U+10991 Meroitic Hieroglyphic Letter Kha

The Wikipedia has the following information about this codepoint:

The Meroitic script consists of two alphasyllabic scripts developed to write the Meroitic language at the beginning of the Meroitic Period (3rd century BC) of the Kingdom of Kush. The two scripts are Meroitic Cursive, derived from Demotic Egyptian, and Meroitic Hieroglyphs, derived from Egyptian hieroglyphs. Meroitic Cursive is the most widely attested script, constituting ~90% of all inscriptions, and antedates, by a century or more, the earliest surviving Meroitic hieroglyphic inscription. Greek historian Diodorus Siculus (ca. 50 BC) described the two scripts in his Bibliotheca historica, Book III (Africa), Chapter 4. The last known Meroitic inscription is the Meroitic Cursive inscription of the Blemmye king, Kharamadoye, from a column in the Temple of Kalabsha (REM 0094), which has recently been re-dated to AD 410/ 450 of the 5th century. Before the Meroitic Period, Egyptian hieroglyphs were used to write Kushite names and lexical items.

Though the Kingdom of Kush ended with the fall of the royal capital of Meroë, use of the language and Cursive script continued for a time after that event. During the 6th century Christianization of Nubia, the Kushite language and Cursive script were replaced by Byzantine Greek, Coptic, and Old Nubian. The Old Nubian script, derived from the Uncial Greek script, added three Meroitic Cursive letters: ⟨ne⟩, ⟨w(a)⟩, and possibly ⟨kh(a)⟩, for Old Nubian [ɲ], [w – u], and [ŋ] respectively. This addition of Meroitic Cursive letters suggests that the development of the Old Nubian script began at least two centuries before its first full attestation in the late 8th century and/or that knowledge of the Kushite language and script was retained until the 8th century.

The script was deciphered in 1909 by Francis Llewellyn Griffith, a British Egyptologist, based on the Meroitic spellings of Egyptian names. However, the Meroitic language itself remains poorly understood. In late 2008, the first complete royal dedication was found, which may help confirm or refute some of the current hypotheses.

The longest inscription found is in the Museum of Fine Arts, Boston.