The story
Indict — to formally charge someone with a crime — came into Middle English from Old French enditer, "to dictate, to write down", and was spelled enditen or endyten. That is the word as it is still pronounced: in-DITE.
The French word came from Late Latin indictare, related to dictare, "to say, to dictate" (as in dictate and dictionary). Later writers reshaped the English spelling to look like the Latin, changing en- to in- and inserting a C. Only the spelling moved; the C has never been pronounced.
The original spelling survives in a twin word, indite, "to write or compose" — rare today, but said exactly like indict. Same word, two spellings, one pronunciation.
