Cud (noun)

1. A portion of food that is brought back into the mouth to be chewed again, typically by ruminants such as cows, sheep, and goats.
2. Something that is constantly repeated or thought about in a contemplative manner.

Origin:

From old english cudu, from proto-germanic *kudô.

Examples:

1. The cow was chewing her cud in the field.
2. He was lost in thought, his mind constantly returning to the same cud.
3. Ruminants like cows and sheep need to chew their cud to fully digest their food.
4. He couldn't shake the cud of worry that had taken root in his mind.
5. The cud of tobacco in his cheek was a constant companion.