Antonyms of adj round-backed

1 sense of round-backed

Sense 1
hunched, round-backed, round-shouldered, stooped, stooping, crooked -- (having the back and shoulders rounded; not erect; "a little oldish misshapen stooping woman")

INDIRECT (VIA unerect) -> erect, vertical, upright -- (upright in position or posture; "an erect stature"; "erect flower stalks"; "for a dog, an erect tail indicates aggression"; "a column still vertical amid the ruins"; "he sat bolt upright")

Similarity of adj round-backed

1 sense of round-backed

Sense 1
hunched, round-backed, round-shouldered, stooped, stooping, crooked -- (having the back and shoulders rounded; not erect; "a little oldish misshapen stooping woman")
       => unerect (vs. erect) -- (not upright in position or posture)