Quick definitions from WordNet (straight-backed)
▸ adjective: of posture ("A slim straight-backed dancer")
▸ adjective: having a straight back ("A straight-backed wooden chair")
▸ adverb: in a straight-backed manner
▸ adjective: of posture ("A slim straight-backed dancer")
▸ adjective: having a straight back ("A straight-backed wooden chair")
▸ adverb: in a straight-backed manner