Answer: trigraph

AnswerCrossword Clue
TRIGRAPHThree letters forming a single sound
TRIGRAPHThree letter simplw sound, e.g. eau
TRIGRAPHCluster of letters, like "sch"
TRIGRAPHCluster of three letters
trigrapha combination of three letters for one sound
trigraphgroup of three letters representing a single speech sound, as eau in beau