Английский Этимологический словарь - ch

- used in O.Fr. for the "tsh" sound. Introduced to Eng. after the Norman Conquest, in words borrowed from O.Fr. such as chaste, charity, chief, etc. Under influence of the French, the digraph was also inserted into O.E. words that had the same sound, such as bleach, and into those that had formerly been spelled with a -c- and pronounced "k" such as chin, much. But 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, chivalry, etc.). It also turns up in words from classical languages (chaos, echo, etc.). Most uses of -ch- in Roman L. were in words from Gk., which would be pronounced correctly as "k" + "h," as in blockhouse, but most Romans would have said merely "k." Sometimes the -h- was written to keep the -c- hard before a front vowel, as still in modern Italian. In some French dialects including that of Paris, Latin ca- became French "tsha," whence the old French (and, after 1066, English) spelling ch- for "tsh."