The word ᴱN. muig “cat” appeared in Early Noldorin Word-lists of the 1920s (PE13/150). In the Gnomish Lexicon of the 1910s, Tolkien instead had G. {mio >>} miog “cat”, along with masculine and feminine variants miaug or miog “tom cat” and {miauli >>} miaulin “she-cat”. The derivation of these early forms isn’t clear.
Neo-Sindarin: I would retain ᴺS. muig “cat” for purposes of Neo-Sindarin, derived from ᴹ√MIW “whine” via an abnormal vocalization: m(i)wikē > mu̯ike > muig. Elaran pointed out that a more normal development would be ✱mŷg < miukē.
A word for “cat” in the Declension of Nouns from the early 1930s, from primitive {mauı̯ǝ >>} miuı̯ǝ (PE21/12-13), and so probably related to the root ᴹ√MIW “whine” from The Etymologies which had the derivative ᴹQ. miule “whining, mewing” (Ety/MIW). The stem form of this “cat” word is the rather unusual miuy-.
Conceptual Development: In the Qenya Lexicon and Poetic and Mythological Words of Eldarissa of the 1910s, the word for “cat” was ᴱQ. meoi (QL/61; PME/61), as in ᴱQ. Vardo Meoita “Prince of Cats” (LT2/15), a sobriquet of ᴱQ. Tevildo. In Early Qenya Word-lists of the 1920s, Tolkien instead gave ᴱQ. yaule “cat”, probably an onomatopoeic word as suggested by Patrick Wynne and Christopher Gilson (PE16/132).
Neo-Quenya: In PPQ (PPQ) from the early 2000s, Terry Dock suggested the neuter, feminine and masculine neologisms for “cat”: ᴺQ. miura, ᴺQ. miurë, and ᴺQ. miuro. However, this predates the publication of ᴹQ. miue “cat”, and I would recommend just sticking with the attested form.