fanqie; traditional Chinese character pronunciation notation
Technical term in Chinese historical phonology. The system uses two characters to indicate the pronunciation of a third: the first character gives the initial consonant (onset), and the second gives the rhyme and tone.
Fanqie is a traditional method that combines two Chinese characters to indicate the pronunciation of a kanji.
The fanqie for 東 is 徳紅切, taking the initial of 徳 and the rhyme and tone of 紅.