'esoterica' originates from Greek, specifically the word 'esōterikos' (ἐσωτερικός), where the root 'esō' (ἔσω) meant 'within' or 'inner'.

'esoterica' passed into Neo-Latin and Modern Latin usage (as plural neuter forms like 'esoterica') from the Greek 'esōterikos', then entered English preserving the plural/mass sense of materials or knowledge intended for an inner circle.

Initially it related to the idea of being 'inner' or 'within' a small group; over time it came to mean the specialized, obscure knowledge or items themselves rather than simply 'inner'.