Name of Emyn Duir after it became the haunt of evil creatures, translated “Mountains of Mirkwood” (UT/280), but more literally “Mountains under Night” (UTI/Emyn-nu-Fuin). This name is a combination of the plural of amon “hill”, the preposition nu “under” and the noun fuin “night”.
Sindarin
Emyn-nu-Fuin
noun. mountains under night
emyn-nu-fuin
place name. Mountains of Mirkwood, (lit.) Mountains under Night
emyn (pl. of amon “hill”) + nu (“under”) + fuin (“dead of night, gloom, darkness”)