せもたれ
back (of a chair); backrest
Common word Also written 背凭れ
Noun
背せもたれもっと倒せるよ。
That seat reclines further.
まず目めに飛とび込こんできたのは、大おおきなソファだ。渋しぶい色いろの革張かわばりで、座面ざめんも背せもたれもゆったりしている。
The first thing that came to my attention was the large sofa. It was covered in sober-coloured leather, and the seat and the back both looked wide and comfortable.