Technical term for a stopper or plug used in laboratory glassware, such as a ground glass stopper.
フラスコに共栓をして、溶液を保存する。
Put a stopper on the flask and store the solution.
Compound of 共 (とも, 'together, matching') and 栓 (せん, 'stopper, plug'), referring to a stopper that fits precisely into a matching joint.