10th cent. From Late Latin cattus 'id.' The voicing of Latin /k/ to Spanish /g/ is unexplained.
Borrowed from an Afro-Asiatic source (compare Coptic klít "cat").
Listed by Tibón (1988) as a particularly ancient hypocorism for physically-gifted individuals who showed agility and cat-like reflexes. The nickname fossilized as the surnames Gato, Gatón, and Gata.
Western Vulgar Latin: Asturian gatu, Portuguese gato, Galician gato, Catalan gat, French chat, Italian gatto; Eastern Vulgar Latin: Aromanian cãtushe, Romanian cătușă; Sardinian: batu; Extra-Comparanda: Basque katu "cat," (dialects) gat(h)u 'id.,' both borrowed from Late Latin cattus
All borrowed from Latin cattus. Old Irish catt "cat," Welsh cath 'id.,' Cornish kath 'id.'
Proto-Germanic *kattu- "cat," which may be borrowed from Latin cattus or borrowed from another language. North Germanic: Old Norse kǫttr "cat;" West Germanic: Old High German kazzo "cat," Old Saxon katto 'id.,' Old Frisian katte 'id.,' Old English catt (English cat)
Borrowed from either Latin cattus or Proto-Germanic *kattu-. East Slavic: Russian kot "tomcat;" Baltic: Lithuanian katė̃ "cat"
Ancient Greek κάττα (kátta) "cat," Modern Greek γάτα (gáta) 'id.'
Borrowed from an unknown language. Old Armenian katu "cat"
Possibly borrowed from another language. Arabic qiṭṭ "cat," Syriac qaṭṭu 'id.'
The sound shift of /k/ to /g/ did not affect c-initial words in Latin, so we are left with the question of whence the g- in gato? Considering cognates in Catalan gat and Italian gatto, we could reconstruct a Vulgar Latin variant *gattus but this looks unmotivated. To posit that the word was borrowed from another language (Basque?) would be at odds with the historical record.