A word for “cow” in the Gnomish Lexicon of the 1910s with deleted variant {mui}, a feminine form of G. mû “ox” (GL/58).
Gnomish
gach
noun. milch cow
mûs
noun. cow
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 in the Gnomish Lexicon of the 1910s appearing as {gacha “cow” >>} G. gach “a milch cow”, cognate to ᴱQ. yakse of the same meaning (GL/36), which was derived from the early root ᴱ√Ẏak “a head of cattle” (QL/105).
Neo-Sindarin: I would retain this word in Neo-Sindarin as ᴺS. gach “cow” (< ✱gyaksē) based on the Neo-Root ᴺ√GYAK, with the sound changes (a) gy- > g- and (b) ks > ch.