起子 is a highly polysemous noun covering several unrelated meanings. In baking, it refers to baking powder (泡打粉). As a tool, it can mean screwdriver or bottle opener, though in standard Mandarin the more common terms are 螺丝刀 and 开瓶器. Figuratively, 起子 can mean prospects, future, courage, or guts (e.g., 没起子 'no future' or 'gutless'). It is also used as a noun for a batch, lot, or group (e.g., 一起子东西), but this sense is less common. The different meanings are entirely context-dependent and not interchangeable.