The Spanish word 'gato' meaning 'cat' comes from the Latin word 'cattus', which meant 'wild cat'. The evolution from Latin 'cattus' to Spanish 'gato' shows a common sound change pattern in the development of Spanish from Latin, where the initial 'c' sound became 'g', and the double 't' simplified to a single 't'.

Since 'gato' is already a basic and commonly used Spanish word, there aren't any simpler Spanish words that derive from the same root. However, you'll find this word in common Spanish expressions like 'llevarse como perros y gatos' (to fight like cats and dogs) and 'gato por liebre' (literally 'cat for hare', meaning to be deceived).

The English word 'cat' is actually related to Spanish 'gato', as they both derive from the Latin 'cattus'. While Spanish developed the initial 'g' sound, English maintained the 'c/k' sound. You can also see this connection in related English words like 'cattery', 'catlike', and 'catalytic' (though this last one has a different Greek origin). The word 'cat' appears in many European languages with similar forms, showing how widespread domestic cats became throughout Europe.