- A single, relatively large quantity of a substance, usually one intended for therapeutic use, such as a bolus dose of a drug injected intravenously.
- A masticated morsel of food or another substance ready to be swallowed, such as a bolus of barium for radiographic studies.
- In high-energy radiation therapy, a quantity of tissue-equivalent material placed in the radiation beam, over the surface of the irradiated region, to increase the absorbed dose in the superficial tissues.
[L. fr. G. bōlos, lump, clod]