“Downright” is a compound word (“down” and “right”) that serves as a particular kind of modifier because it can serve as both an adjective and an adverb. It modifies either a noun or an adjective, as follows: “It’s a downright shame” (an adjective modifying the noun “shame”) or “It’s downright shameful” (an adverb modifying the adjective “shameful”). Its main meaning is “absolute,” “plain,” or “undeniable.” Long ago, it also meant “looking straight downward.” But that meaning is now obsolete. In informal speech, it emphasizes a non-contestable speech utterance. It is seldom used in formal or legal language because it is rhetorical rather than provable. Any responder can argue that the contested statement is in fact deniable, as in "You say his tattoos are downright shameful, but in many cultures body decoration is considered beautiful."