'diagram' originates from Greek, specifically the word 'diagramma,' where 'dia-' meant 'through' and 'graphein' meant 'to write.'

'diagramma' transformed into the Latin word 'diagramma,' and eventually became the modern English word 'diagram' through Middle English.

Initially, it meant 'a figure marked out by lines,' but over time it evolved into its current meaning of 'a simplified drawing or representation.'