Herumor means "Black Lord" in Quenya (from heru = "lord" and morë = "dark").
Quenya
herumor
masculine name. *Black Lord
Elements
Word Gloss heru “lord, master” morë “dark, black; darkness, night, dark, black; darkness, [ᴹQ.] blackness, [Q.] night”
herumor
Herumor
An evil Númenórean leader of the Haradrim at the end of the Second Age (S/293). His name seems to be a compound of heru “lord” and morë “black”. The name is translated “Black Númenórean” by Christopher Tolkien (PMI/Herumor) but a more literal translation would be “✱Black Lord”.