from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Three letters spelling one consonant, vowel, or diphthong, such as Sch in Schiller or igh in high or thigh.
- n. A group of three letters, especially of frequent occurrence in a given language, as the or ing in English or gli in Italian.
- n. Any combination of three letters of an alphabet. Also called trigram.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A specific sequence of three letters, especially one used collectively to represent a single phoneme.
from the GNU version of the Collaborative International Dictionary of English
- n. Three letters united in pronunciation so as to have but one sound, or to form but one syllable, as -ieu in adieu; a triphthong.
from The Century Dictionary and Cyclopedia
- n. A combination of three letters to represent one sound; a triphthong, as eau in beau.
tri- + -graph (Wiktionary)