Middle Primitive Elvish
kem
root. soil, earth
kēm
noun. *earth
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.
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.
This root was established as the basis for “earth” words early in Tolkien’s writing. It first appeared as ᴱ√KEME “soil” in the Qenya Lexicon of the 1910s, its most notable Qenya derivative being ᴱQ. kemen “soil, earth” (QL/46). The root ᴹ√KEM “soil, earth” reappeared in The Etymologies of the 1930s along with ᴹQ. kén (kem-) or kemen “earth”, as well as various other Quenya and Noldorin derivatives (Ety/KEM). Tolkien’s continued use of Q. cemen and S. ceven for “earth” or “the Earth” in later writings indicates the continued validity of this root.