Definition of "sourdough"

A type of bread dough leavened with yeast and lactobacilli that produce acids giving a sour taste.  examples

(countable, slang) An old-timer, especially in Alaska.  quotations

(countable, Yukon) A permanent resident of the territory. Someone who has lived in the Yukon during all four seasons.  examples

(countable, historical) A 49er, a California Gold Rush miner.

(obsolete) Leaven; an agent that makes dough rise.