wormwood: a bitter desert shrub, used in the Bible only as an image of ruinous bitterness, the taste of judgment or of justice gone poisonous
Wormwood is a low grey shrub of the desert, almost certainly the plant botanists now call white wormwood, and its sap is famously bitter. The Bible never shows it growing in a field, never uses it as medicine, and never puts it in a meal. All eight times the word appears it is an image: something so bitter that being made to swallow it means ruin.
Five of those eight verses set it beside another bitter plant word, רֹאשׁ, usually rendered "poison" or "gall". The pairing starts in the covenant warnings of Deuteronomy, where anyone who quietly turns to other gods is a root growing poison and wormwood inside the community. Jeremiah takes the same pair up as a threat: God will feed this people wormwood and give them poisoned water to drink. In Lamentations the survivor of Jerusalem's fall says it of himself, remembering the wormwood and the poison he has been made to swallow.
Amos uses the word differently. There it is not a drink forced on the guilty but what corrupt courts have made of something good: judges have turned justice itself to wormwood, so that what should have fed a nation now poisons it. Amos was speaking to people who knew the Deuteronomy warning, and hearing "wormwood" from a prophet told them the curse was already at work among them.
One passage stands slightly apart. Proverbs uses the taste as a warning about a tempting path: what begins sweet ends bitter as wormwood and sharp as a two-edged sword. Even there the point is the ruin waiting at the end, not merely an unpleasant flavor.