The term beast can mean any animal, but is usually taken to mean any large land animal. The term beast of burden is used to describe any large animal that is put to work by humans, such as an ox that is used to plough fields.
A feast is similar to a banquet but is less formal. A feast is a very large, extravagant meal for any number of people. You can prepare a feast just for yourself if you want to.
Yeast is a very tiny fungal organism. Some species of yeast are used in baking and brewing. Yeast can make bread rise and become light and fluffy, and it can be used to make some wines and beers.
Yeast extract is used to make some very strongly flavoured spreads like Vegemite.
