Middle Primitive Elvish
sud
root. base, ground
stud
root. base, ground
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.
The root ᴹ√SUD “base, ground” appeared in The Etymologies of the 1930s with derivative ᴹQ. sundo “base, root, root-word” (Ety/SUD), but it was given an alternate form ᴹ√STUD with Noldorin forms like {N. sunn >>} N. thund/thonn being added to the entry (EtyAC/SUD). Tolkien’s later of use of S. thond “root” (< ✱stundā?) in S. Morthond “Blackroot” implies the ongoing validity of this root (LotR/1115). In The Etymologies, Tolkien’s first attempt at the basis for “root” words was a deleted entry {ᴹ√NDUM/DUM >>} ᴹ√NDUB/DUB “lay base, foundation, root; found” (EtyAC/NDUB).