downright

The adverb is derived from Middle English dounright, dounriȝt (“right down, straight down; face down; vertically; used for emphasis: outright, downright”), and then either:

possibly an aphetic form of adounright (“straight down; directly, immediately (?)”), from adoun (“downward”, adverb) (from Old English adūn, adūne (“down, downward”, adverb), ultimately from dūn (“hill, mountain”), from Proto-West Germanic *dūnā, *dūnu (“hill; sand dune”), possibly from Proto-Indo-European *dʰewh₂- (“haze, mist; smoke”)) + right (“direct; straight; etc.”, adjective) (from Old English riht (“straight; etc.”), ultimately from Proto-Indo-European *h₃reǵ- (“to straighten”)); or

from doun (“down, downward; etc.”, adverb) (from Old English dūne (“down”), ultimately from dūn (“hill, mountain”): see above) + right.

By surface analysis, down (adverb) +‎ right (adjective).

The adjective and noun are derived from the adverb. Noun sense 1 (“low grade of wool”) may be from the obsolete adjective sense 2.2 (“in its most basic form; ordinary”).