What is a gill of yeast as used in recipes from the Colonial Era?

A gill is a half cup. A gill of yeast would have been a half cup of brewed yeast or beer.

Colonial era housewives, often called ale wives, would brew the beer or ale for consumption by the whole family. Yeast was necessarily grown in this manner for use in bread making as well as ale or beer making, often in a cool room adjoining the kitchen, so that a gill of yeast would have been a half cup of this brew kept fermenting for this purpose.

Today's equivalent would be about a tablespoon of active dry yeast.