Unrighteous, a. — Webster enters it under “unrighteous”
Etymology: [OE. unrightwise, AS. unrihtwis. See Un- not, and Righteous.]
1. Not righteous; evil; wicked; sinful; as, an unrighteous man.
2. Contrary to law and equity; unjust; as, an unrighteous decree or sentence. -- Un*right"eous*ly, adv. -- Un*right"eous*ness, n.
Shades of meaning
Fernald has no entry of its own for unrighteousness; he lists it under injustice, sin.
Where he writes about it:
"All unrighteousness is sin," 1 John v, 17. — from sin