'index' originates from Latin, specifically the word 'index' (from the stem 'indic-'), where the root is related to 'indicare' meaning 'to point out' or 'to indicate'.

'index' passed from Latin into Old French and then into Middle English as 'index', eventually becoming the modern English word 'index'.

Initially it meant 'one who points out' or 'a sign that indicates'; over time it evolved into the current senses of 'a list or table of contents/entries' and 'a numerical indicator'.