Sigmund Freud’s original term for the unconscious mind was not id but es, the indefinite pronoun it in German.
Freud borrowed that term from a physician, Georg Groddick, who in turn had borrowed it from his teacher Ernst Schweninger.
As Freud’s ideas became popular in English-speaking countries, translators felt that simply calling the unconscious it was too vague and unscientific.
They replaced it with its Latin translation, id.