'mediumistic' originates from Latin, specifically the word 'medium', where 'medium' meant 'middle' or 'an intermediate agency', combined with the suffix '-istic' (from Greek '-istikos' via French/English) meaning 'pertaining to'.

'mediumistic' formed in English by combining the noun 'medium' (borrowed from Latin) with the adjective-forming suffix '-istic'; the adjective gained usage in the 19th century within spiritualism to describe things relating to mediums and mediumship.

Initially it meant 'pertaining to a medium' in a general or literal sense; over time it became specialized to describe characteristics, abilities, or phenomena associated with spiritualist mediums (current meaning: 'relating to or characteristic of mediumship').