The word "just" can be used as an adjective, adverb, or noun. As an adjective, it means fair, morally right, or appropriate. As an adverb, it can mean 'only' or 'merely', signifying something that is restricted in degree or amount, or it can indicate that something is done very recently. When used as a noun, it refers to a person who acts up to moral principles or standards.
The word "just" traces back to the Latin word "justus," which means "lawful, just, or righteous." It entered the English language through Old French "juste," which carries similar meanings.