The word zenith is a mistake. It came to be because Medieval lettering was not exactly optimal.
Latin scribes misread the Arabic expression سمت الرأس, samt ar-as (meaning “path above the head”) as sanit, since “m” and “ni” looked practically the same in old manuscripts. And from Latin the erroneous transcription spread to most other European languages.
If you ever worried about having bad calligraphy, think of it as inspiring new words for generations to come.
You can get more information about the etymology on Wikipedia or Wiktionary.
Originally published in The blind mouse.