In a bitter argument or conflict, people argue very angrily or fight very fiercely.

If someone is bitter after a disappointing experience or after being treated unfairly, they continue to feel angry about it.

A bitter experience makes you feel very disappointed. You can also use bitter to emphasize feelings of disappointment.

Bitter weather, or a bitter wind, is extremely cold.

A bitter taste is sharp, not sweet, and often slightly unpleasant.

Bitter is a kind of beer that is light brown in colour.

If you say that you will continue doing something to the bitter end, especially something difficult or unpleasant, you are emphasizing that you will continue doing it until it is completely finished.