二级头 èrjítóu second stage Origin Definitions Defs Strokes Stroke Words Sentences Sents 二级头呼吸器 èrjítóuhūxīqì regulator; demand valve (scuba diving) second-stage regulator; a device that reduces air pressure to a breathable level upon inhalation备用二级头呼吸器 bèiyòng'èrjítóuhūxīqì octopus (scuba diving) a backup regulator or secondary air source used for emergencies