trigram

noun3

1. •
   An n-gram consisting of three items from a sequence.

   • In fact, half of all such words for this corpus are initiated by only 39 different trigrams! — 1974
2. •
   Any of the eight combinations of three complete or broken lines forming half of a hexagram in Chinese system of divination I Ching.
3. •
   A trigraph, a sequence of three letters representing one phoneme.