What is the meaning of Sourdough?

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

An old-timer, especially in Alaska.

A permanent resident of the territory. Someone who has lived in the Yukon during all four seasons.

A 49er, a California Gold Rush miner.

Leaven; an agent that makes dough rise.

Source: wiktionary.org