'intra-galaxy' is formed from the Latin prefix 'intra-' meaning 'within' and the noun 'galaxy' (from Greek 'galaxias').

'galaxy' comes from Greek 'galaxias' (related to 'gala' meaning 'milk'), passed into Late Latin and Old French, then into Middle English as 'galaxie', and eventually became modern English 'galaxy'. The combining form 'intra-' is from Latin 'intra' meaning 'within; inside'.

Initially, components referred specifically to 'within' (Latin 'intra-') and the Milky Way (Greek 'galaxias'), but the combined form now describes anything occurring inside any galaxy, not just the Milky Way.