Downright means thoroughly, and it is used of things that are bad. Downright rude, downright dangerous, downright lies.
It is an intensifier that only attaches to negatives — downright rude and downright dangerous are ordinary, and downright kind is not. As an adjective it means the same before a noun: downright nonsense. Note that it is one of a small set of intensifiers with a built-in polarity, like utterly and stark; and that down here means completely rather than downward, as it does in downpour.
1adverbdownrightThoroughly, said of something bad.
“It's downright rude to look at your phone while someone is talking to you.”
synonyms: utterly, thoroughly
downright is a degree of thoroughness.
Middle English dounright meant straight down, and the sense of thoroughness came from the idea of a blow struck straight down — complete rather than glancing.
Proto-Indo-European
*dʰewh₂-
Middle English
dounright
English, today
downright
Built from
The is derived from Middle English dounright, dounriȝt (“right down, straight down; face down; vertically; used for emphasis: outright, downright”), and then either:
Etymology from Wiktionary, CC BY-SA