'Bitter' in the Bible

making their lives bitter through hard labor with mortar, bricks, and all kinds of outdoor labor. They ruthlessly imposed all this work on them.

That very night they're to eat the meat, roasted over the fire, with unleavened bread and bitter herbs.

When they came to Marah, they could not drink the water at Marah because it was bitter. (That is why it's called Marah.)