Early Primitive Elvish
mṛðṛ
root. grind
mṛřṛ
root. grind
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.
A root in the Qenya Lexicon of the 1910s given as ᴱ√MṚŘṚ with derivatives like ᴱQ. mar (mard-) “grit, course grain or powder”, ᴱQ. mard- “grind, pulverize” and ᴱQ. marma “sand” (QL/63). In a list of roots at the end of the M-section, ᴱ√MṚÐṚ was gloss “grind” (QL/63). Early in the M-section Tolkien had the root {ᴱ√MAŘA² >>} ᴱ√MARA as a dialectical variation or byform of ᴱ√MṚŘṚ, with the derivative ᴱQ. marilla “pearl” (QL/59); see that entry for details. The Gnomish cognate of ᴱQ. marilla was given as G. brithla “pearl” in the contemporaneous Gnomish Lexicon (GL/24), and this Gnomish word probably a derivative of ᴱ√MṚÐṚ. In that document these words served as the base for ᴱQ. Silmaril and its Gnomish equivalent G. Silubrilt (GL/67). There are no signs of this root in Tolkien’s later writing, and Q. Silmaril was given different etymologies later on.