Further etymology and cognates.
The Germanic word is generally thought to be from Late Latin cattus (“domestic cat”) (c. 350, Palladius), from Latin catta (c. 75 A.D., Martial), from an Afroasiatic language. This would roughly match how domestic cats themselves spread, as genetic studies suggest they began to spread out of the Near East / Fertile Crescent during the Neolithic (being in Cyprus by 9500 years ago, and Greece and Italy by 2500 years ago), especially after they became popular in Egypt. However, every proposed source word has presented problems. Adolphe Pictet and many subsequent sources refer to Barabra (Nubian) (kaddîska) and "Nouba" (Nobiin) kadīs as possible sources or cognates, but M. Lionel Bender says the Nubian word is a loan from Arabic قِطَّة (qiṭṭa). Jean-Paul Savignac suggests the Latin word is from an Egyptian precursor of Coptic ϣⲁⲩ (šau, “tomcat”) suffixed with feminine -t, but John Huehnergard says "the source was clearly not Egyptian itself, where no analogous form is attested."
It may be a Wanderwort. Kroonen says the word must have existed in Germanic from a very early date, as it shows morphological alternations, and suggests that it might have been borrowed from Uralic, compare Northern Sami gađfe (“female stoat”) and Hungarian hölgy (“stoat; lady, bride”) from Proto-Uralic *käďwä (“female (of a fur animal)”).
Related to Scots cat, West Frisian kat, North Frisian kåt and kaat, Dutch kat, Danish kat, Norwegian katt, Swedish katt, German Low German Katt and Katte, German Katze, Alemannic German Chatz, Icelandic köttur, Afrikaans kat, Latin cattus, French chat, Norman cat, Occitan cat, Portuguese gato, Spanish gato, Aromanian cãtush, Scottish Gaelic cat, Irish cat, Breton kazh, Welsh cath, Cornish kath, as well as Ancient Greek κάττα (kátta), Greek γάτα (gáta), and from the same ultimate source Russian кот (kot), Ukrainian кіт (kit), Belarusian кот (kot), Polish kot, Kashubian kòt, Lithuanian katė, and more distantly Armenian կատու (katu), Basque katu, Hebrew חתול (khatúl), Arabic قِطَّة (qiṭṭa) alongside dialectal Maghrebi Arabic قَطُّوس (qaṭṭūs) (from Berber, probably from Latin).