Originally Posted by Linkster

A trigraph is a combination of three letters representing one sound. An example is eau as in bureau.
A subvocal is beneath the voice, a silent or nearly silent sound.
A dighthong is a complex vowel sound made by gliding continuously from the position of one vowel to that for another within the same same syllable. An example is (ou) as in down.
Cognate letters are related in derivation, for instance, i and y.
Linguals are sounds articulated by using the tongue, for instance the sound th

yeah I cheated