couchette
/kuːˈʃet/noun
1- a railway carriage with seats convertible into sleeping berths（铁路上的）坐卧两用车厢。
1.1
- a berth in such a carriage（坐卧两用车厢内的）座位。
词源
1920s: French, literally 'little bed', diminutive of couche 'a couch'.