small deep dish; dice cup
Refers to a small, deep dish, often used for holding soy sauce or other condiments, or as a dice cup in games.
I put soy sauce in a small deep dish and ate sashimi.
博打で壺皿を振って賽を投げる。
In gambling, you shake the dice cup and throw the dice.
Compound of 壺 (tsubo, 'jar, pot') and 皿 (sara, 'dish, plate'), referring to a dish that is deep like a small pot.