A thyrsus /ˈθɜːrsəs/ or thyrsos /ˈθɜːrˌsɒs/ (Ancient Greek: θύρσος) was a wand or staff of giant fennel (Ferula communis) covered with ivy vines and leaves, sometimes wound with taeniae and topped with a pine cone or by a bunch of vine-leaves and grapes or ivy-leaves and berries, carried during Hellenic festivals and religious ceremonies. The thyrsus is typically associated with the Greek god Dionysus, or his Roman counterpart Bacchus, and represents a symbol of prosperity, fertility, and hedonism similarly to Dionysus.

In Greek religion, the staff was carried by the votaries of Dionysus. Euripides wrote that honey dripped from the thyrsos staves that the Bacchic maenads carried. The thyrsus was a sacred instrument at religious rituals and fêtes.

The fabulous history of Bacchus relates that he converted the thyrsi carried by himself and his followers into dangerous weapons, by concealing an iron point in the head of leaves. Hence his thyrsus is called "a spear enveloped in vine-leaves", and its point was thought to incite to madness.