1.
sake cup, ceremonial cup
A small, flat, dish-shaped cup used for drinking sake. Traditionally made of lacquerware or ceramic. Strongly associated with ceremonial occasions such as weddings, New Year celebrations, and formal pledges.
Usage
Carries a formal, ceremonial nuance. The phrase 盃を交わす (to exchange cups) implies forming a bond or pledge — historically used in rituals of loyalty, brotherhood, or marriage. In everyday drinking, おちょこ or 猪口 is more common for the small cup.
Writing
The character 盃 combines 不 and 皿 (dish). An older form 杯 exists and is used in counting cups (一杯).