[mass noun]leaven for making bread, consisting of fermenting dough, originally that left over from a previous baking 酵头 ■bread made using such leaven 用酵头制成的面包
(N. Amer.)an experienced prospector in the western US or Canada; an old timer (北美)(美国西部或加拿大)有经验的探矿者;老居民,老职员,老手