tetragram

noun

1. A group of four letters.
2. In the Taixuanjing, a sequence of four lines, each of which may be unbroken, broken once, or broken twice. Each sequence is interpreted as an element of the sets of solid lines (⚊ for Heaven), once-broken lines (⚋ for Earth) and twice-broken lines (𝌀 for Man) formed by combinations of four monograms (two digrams or bigrams, in other words) in the divination of the Taixuanjing.