'intragalactic' originates from a combination of Latin and Greek, specifically the Latin prefix 'intra-' and the Greek word 'galaxias', where 'intra-' meant 'within' and Greek 'gala' (in 'galaxias') meant 'milk'.

'galaxy' comes from Greek 'galaxias' (γαλαξίας) 'milky (circle)', passed into Latin and Old French, then Middle English 'galaxie'; 'galactic' was formed from that root in modern English, and the Latin prefix 'intra-' was later attached to create 'intragalactic'.

Initially references to the 'galaxy' historically often meant the Milky Way specifically; over time 'galaxy' came to mean any such island of stars, so 'intragalactic' shifted from 'within the Milky Way' to 'within any given galaxy.'