1. Meroitic: This is the most likely candidate. It was a written language used in Kush from around the 3rd century BCE to the 4th century CE. Meroitic script is similar to Egyptian hieroglyphs, but the language itself is distinct and unrelated to Egyptian. It is still largely undeciphered, though scholars have made progress in understanding some words and phrases.
2. Old Nubian: This language, which is related to Egyptian, was spoken in Nubia (the region encompassing Kush) from around the 4th century BCE onward. Old Nubian is much better understood than Meroitic, but its use in Kush is less certain. Some scholars believe that Old Nubian might have been spoken alongside Meroitic, perhaps as a language of everyday life, while Meroitic was used for official purposes.
3. Other possibilities: There's a chance that other languages were spoken in Kush as well, particularly in different regions or during different periods. This includes the possibility of dialects of other Nubian languages, languages related to Cushitic or Afro-Asiatic language families, or even languages from other regions that were brought in through trade or migration.
In summary: While Meroitic is the most likely language of the ancient Kingdom of Kush, we don't have a complete understanding of the language landscape of the region. Further research and archaeological discoveries are needed to shed more light on the languages spoken in Kush.