Buttermilk (noun)

1. A thin, sour-tasting milk that is a by-product of the butter-making process, made by adding bacteria to low-fat or skim milk.
2. A beverage made from buttermilk.

Origin:

From old english butere and meoluc, both meaning 'butter' and 'milk' respectively.

Examples:

1. She poured the cold buttermilk over her cereal.
2. I love to drink buttermilk on a hot summer day.
3. Adding buttermilk to a recipe makes the finished product tender and flaky.
4. Buttermilk is an essential ingredient in Southern-style fried chicken.
5. A buttermilk biscuit is a staple in Southern cuisine.