A noun used in the Namárië poem and loosely translated as “deep in shadow” (LotR/377), but more accurately “heavy shadow, dark shadow” (PE17/72, 168; RGEO/59). It is a derivative of the root √LUB “shadow” (PE17/168), perhaps an elaboration of ᴹQ. lumbe “gloom, shadow” from The Etymologies of the 1930s (Ety/LUM).
Neo-Quenya: Based on its use, I suspect lumbulë refers to a great expanse of shadow (“shadowness”) rather than an individual cast shadow, which is Q. hala.
lumbulë noun "(heavy) shadow" (Nam, RGEO:67, PE17:168)