Intended for or understood by only a small group of people with specialized knowledge; secret or mysterious.
From Greek 'esoteros' (inner, inner circle) + '-ical' (adjective suffix). This is a less common variant of 'esoteric,' using the '-ical' ending more typical of formal academic language.
The '-ical' ending was once the standard way to make adjectives in English, which is why you sometimes see 'esoterical' in older texts—it sounds more formal and scholarly, like comparing 'historic' with 'historical.'
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