'ecumenism' originates from Greek, specifically the word 'oikoumenē,' where 'oikos' meant 'house' or 'habitat.'

'oikoumenē' transformed into the Latin word 'oecumenicus,' and eventually became the modern English word 'ecumenism' through Middle English.

Initially, it meant 'the inhabited world,' but over time it evolved into its current meaning of 'promoting unity among Christian churches.'