There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
lusta
adjective. void, empty
kúma
noun. void
A word for “void, darkness”, perhaps first appearing in Ambarkanta from the early 1930s (SM/241). The Etymologies from around 1937 had ᴹQ. kúma “void” under the root ᴹ√KUM of the same meaning (Ety/KUM). It was an element in ᴹQ. Avakúma “Exterior Void”, the darkness surrounding the world (SM/241; Ety/AWA).
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
An adjective in The Etymologies of the 1930s glossed “void, empty” derived from the root ᴹ√LUS (Ety/LUS).