spindle-shaped bacterial cell esp. one swollen at the center by an endospore. [WordNet 1.5]
a genus of anaerobic, spore-forming motile bacteria of the family Bacillaceae, including several pathogenic species, such as the causative agents of gas gangrene (Clostridium perfringens), botulism (Clostridium botulinum), and tetanus (Clostridium tetani). [PJC]