'gnostic' originates from Greek, specifically the word 'gnōstikos', where 'gnōsis' meant 'knowledge'.

'gnōstikos' passed into Late Latin as 'gnosticus' and then into English (via Medieval/early modern scholarly and religious usage) as 'gnostic'.

Initially, it broadly meant 'pertaining to knowledge', but over time it became associated specifically with the religious movement and doctrines of Gnosticism and with claims to special/esoteric knowledge.