血栓
xuè shuān · HSK 7
blood clot
🩸 血 (blood) + 栓 (plug, stopper) = a plug that stops the blood = a clot
栓 shuān is the same character used for a bolt, cork, or stopper that seals a pipe. A 血栓 is literally a blood-stopper: a clump that corks a vessel and halts the flow.
血 — drop 丿 over dish 皿
Originally a pictograph of a sacrificial vessel (皿) with a drop of blood inside, marking the offering of blood in ancient rituals. The small stroke on top represents the blood itself. Over time it broadened from ritual blood to blood in general.