Middle Primitive Elvish
stak
root. split, insert
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.
Early Primitive Elvish
stakta-
verb. to split
Old Noldorin
nestak-
verb. to insert, stick in
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 Etymologies of the 1930s glossed “split, insert” with derivatives like ᴹQ. sanka/N. thanc “cleft, split” and N. nestegi “insert, stick in” (Ety/STAK). S. thanc remained an element in S. Orthanc “Forked Height” (LotR/555; UT/400), indicating the ongoing validity of this root.