Hamnah is an ancient Arabic name that refers to grapes that came from the city of Ta'if near Mecca, black in color with some redness, famous for having tiny seeds.
This name is not a Quranic name (not mentioned in the Quran, and there are no words in the Quran related to it). It is however an Islamic name because some of the Prophet's female Companions were named such. Most famous is Hamnah bint Jahsh [ra], sister of Zaynab [ra], who is one of the wives of Prophet Muhammad [s]. Another Hamnah is Hamnah bint Abi Sufyan, foster niece of Prophet Muhammad [s].