1.
a-un; unspoken mutual understanding; perfect synchronization
Originally a Buddhist term representing the first and last sounds of the Sanskrit alphabet (like alpha and omega), symbolizing the beginning and end of all things. In modern usage, most commonly refers to the tacit, wordless coordination between two people who understand each other perfectly.
Almost always used in the set phrase 阿吽の呼吸 (literally "a-un breathing"), meaning perfect wordless coordination. This phrase describes two people who work together so well they need no verbal communication. The concept originates in Buddhism: 阿 (mouth open, the first sound) represents birth/beginning, and 吽 (mouth closed, the last sound) represents death/ending. At shrines and temples, paired guardian statues (狛犬 or 仁王像) embody this concept, with one figure's mouth open and the other closed.