Rectitude has a righteous derivation. It comes straight from the Latin adjective rectus, which means both "right" and "straight." Rectitude itself can mean either "straightness" (an early use referred to literal straightness of lines, although this sense is now rare) or "rightness" of character.

Is rectitude a noun or adjective?

Rectitude is a noun. A noun is a type of word the meaning of which determines reality.

Is Sharp an adjective?

adjective, sharp·er, sharp·est. having a thin cutting edge or a fine point; well-adapted for cutting or piercing: a sharp knife. terminating in an edge or point; not blunt or rounded: The table had sharp corners.