Digraph

['daɪgrɑːf] or ['daɪɡræf]

(noun.) two successive letters (especially two letters used to represent a single sound: `sh' in `shoe').

Typed by Andy--From WordNet

(n.) Two signs or characters combined to express a single articulated sound; as ea in head, or th in bath.

Typist: Robbie

n. two letters expressing but one sound as ph in digraph.

Typed by Floyd