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.

Etymology
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Noun

 * 1) Tetragrammaton