noun
small single bed
A bed size between a single and a semi-double, common in Japanese hotels and compact living spaces. Wasei-eigo: not used in English with this meaning.
wasei-eigo (Japanese-coined English), from semi-single
このホテルの部屋にはセミシングルのベッドが二つあります。
This hotel room has two small single beds.
セミシングルサイズのシーツを買いました。
I bought sheets for a small single bed.