15th century, at first predominantly in the form fochen. Usually derived from Medieval Latin focō, itself from Latin focus (“hearth”). The -ch- is problematic, however. If it were due to the High German consonant shift, the word would have to be 700 years older than its first attestation. It should not be ruled out that fach, foch may be onomatopoeias for the ignition of a fire and/or the stoker's blowing.