ch

digraph used in Old French for the "tsh" sound. In some French dialects, including that of Paris (but not that of Picardy), Latin ca- became French "tsha." This was introduced to English after the Norman Conquest, in words borrowed from Old French such as chaste, charity, chief (adj.). Under French influence, -ch- also was inserted into Anglo-Saxon words that had the same sound (e.g. bleach, chest, church) which in Old English still was written with a simple -c-, and into those that had formerly been spelled with a -c- and pronounced "k" such as chin and much.

As French evolved, the "t" sound dropped out of it, so in later loan-words from France ch- has only the sound "sh-" (chauffeur, machine (n.), chivalry, etc.).