Radish is a noun. A noun is a type of word the meaning of which determines reality. Nouns provide the names for all things: people, objects, sensations, feelings, etc.

Is radish a proper noun?

A plant of the Brassicaceae family, Raphanus sativus, having an edible root. The pungent root of this plant, usually eaten raw in salads etc.

Is reddish an adjective?

Somewhat red.