The adjective that could be used to describe "un gato" (a cat) is:
c. Pequeño (Small)
A noun or noun phrase is described or defined by an adjective. Its semantic role is to alter the information provided by the noun.
Adjectives have always been regarded one of the primary components of speech in the English language, but they were formerly classified with nouns.
Adjectives enrich language by adding detail and vividness. They characterize nouns, enriching and clarifying communication. Adjectives are used in everyday life to communicate emotions, differentiate between objects, and provide a more complete picture of the world.