Early Quenya
yak(k)o
noun. ox
taruku
noun. ox
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 noun for “ox” appearing in the Qenya Lexicon of the 1910s with variants yakko and yako, derived from the early root ᴱ√Ẏak “a head of cattle” (QL/105). In the contemporaneous Poetic and Mythological Words of Eldarissa Tolkien had yakk- “ox” (PME/105). In Early Qenya Word-lists of the 1920s, the word for “ox” was also yakko (PE16/132).